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Here you will find definitions to common plumbing terminology and other industry related terms to help keep you informed.


  • ABS: Aristocraft Bristone Styrine - A rigid black plastic piping used for waste, vent, and drain lines.
  • Absorption Field: A leeching or seeping field engineered to receive septic tank effluent.
  • Access Panel: An opening in the wall or ceiling near the fixture that allows access for servicing the plumbing/electrical system.
  • Activated Carbon: A water treatment medium, found in block, granulated, or powdered form, which is produced by heating carbonaceous materials, such as coal, wood, or coconut shells, in the absence of air, creating a highly porous adsorbent material. Activated carbon is commonly used for dechlorination, organic chemical reduction and radon reduction, and is recognized by the US EPA as the best available technology for reduction of organic chemicals from drinking water.
  • Adaptor: A fitting that unites different types of pipe together, such as ABS to cast iron pipe.
  • Aerator: A device screwed into the end of a faucet spout that mixes air into flowing water, and controls flow to reduce splashing. It sometimes contains a baffle to reduce flow to 2.5 gallons per minute (gpm).
  • Air Admittance Valve: A device that replaces a traditional vent to allow air to enter the pipe and equalize pressure, preserving the seal of water in the fixture trap.
  • Angle Stop: A shutoff valve between the water pipes and a faucet. Its inlet connects to the water supply pipe in a wall, and its outlet angles up 90 degrees toward the faucet. These are usually used to shut off water to a fixture in case of an emergency repair rather than daily usage.
  • Angular Discharge Tube: A discharge tube that changes the direction of water flow to approximately 90 degrees.
  • Anode Rod: A sacrificial rod installed in a water heater that protects the tank from corrosion, helping to extend the life of the tank.
  • Anti-Scald Valve: Device used to prevent high water temperature.
  • Anti-Siphon: Preventive device for the backflow of liquid into a system. Used on sprinkler systems to prevent water from trickling back into the supply that is feeding it.


  • Back Pressure: Pressure that resists the flow of fluid in a piping system.
  • Backflow: When water travels from one system upstream or back into any part of the main distribution system.
  • Backflow Preventer: A device to prevent water from traveling from one system back into any part of the main distribution system, usually by siphoning, especially into a potable water supply. This is generally required for sprinkler systems, handheld showers, pullout faucet spouts, kitchen sprayers, etc; also known as a check valve.
  • Backup: The overflow of a plumbing fixture due to drain stoppage.
  • Backwash: The up flow or counter-current flow of water through a filter or ion-exchange medium, lifting the mineral bed and flushing away to the drain the particles of foreign matter that have been filtered from the water supply during the service cycle.
  • Backwater Valve: Sewer line valve that prevents sewage from flowing back into the house.
  • Ballcock: The fill valve that controls the flow of water from the water supply line into a gravity-operated toilet tank. It is controlled by a float mechanism that floats in the tank water. When the toilet is flushed, the float drops and opens the ballcock, releasing water into the tank and/or bowl. As the water in the tank is restored, the float rises and shuts off the ballcock when the tank is full.
  • Basin Wrench: A wrench with a long handle, with jaws mounted on a swivel, that allows the jaws to reach and handle nuts to fasten faucets to a previously installed sink.
  • Basket Strainer: A basket-shaped strainer with holes and a slot that fits into a sink or shower drain to allow water to run out but to catch food or other objects before they can enter the sewage system and possibly clog the drain.
  • Bidet: A personal hygiene plumbing fixture similar in appearance to a toilet bowl used for washing genitals and posterior areas of the body. It is mounted on the floor next to a toilet and consists of a washing basin, a hot and cold faucet, and sprayer.
  • Bleed: To drain a pipe, tube, or hose of excess air by opening a valve at the end or systematically removing the air by force or suction.
  • Boiler: A sealed tank where water is heated and turned to steam for power or hot water.
  • Boiling Point: The temperature at which a liquid changes to vapor by the addition of heat.
  • BTU: British Thermal Unit - Unit of heat energy required to raise 1 lb. of water 1°F.
  • Burner: A device in a which a flame or heat is produced in a water heater.


  • Catch Basin: Large underground container, with a grate on the top, for collection of storm water run-off. It catches or collects dirt and other debris and prevents them from polluting streams and lakes.
  • Centerset: Style of bathroom faucet having combined spout and handles, with handles 4 inches apart, center-to-center. Also a single-handle faucet installed on 4 inches center-to-center faucet holes.
  • Check Valve: Allows fluid to flow in only one direction in a pipe; also known as backflow preventer.
  • Chloramines: Chemical complexes formed from the reaction between ammonia and chlorine being used to disinfect many municipal water supplies. Does not combine with organics to form trihalomethanes.
  • Chlorine: Widely used in the disinfection of water and as an oxidizing agent for organic matter, iron, hydrogen sulfide, etc. It is available as a gas, as a liquid in sodium, hypochlorite, or as a solid in calcium hypochlorite. In water chlorine reacts with organics to form trihalomethanes (THM) which can cause cancer.
  • Circuit Vent: Plumbing drainage system vertical vent which is run from the last two traps on a horizontal drain line to the main vent stack of a building drainage system.
  • Cleanout Plug: A plug in a trap or drain pipe that provides access for the purpose of clearing an obstruction.
  • Clevis Hanger: A type of pipe hanger with a swivel yoke supported at the top by an adjustable vertical rod. This yoke bolts to pin holding a U-strap of metal (clevis) that supports the pipe.
  • Closed System: A system where the incoming cold water supply has a device that will not allow water to expand when heated (i.e. check valve, back-flow preventer, some pressure reducing valves, water meters).
  • Closet: A term used for a Toilet.
  • Closet Auger: A flexible rod with a curved end used to access the toilet's built-in trap and remove clogs.
  • Closet Bend: A curved fitting mounted immediately below the toilet that connects the closet flange to the toilet drain.
  • Closet Flange: An anchoring ring that attaches to the closet bend and secured to the floor. The heads of closet bolts, used to secure the toilet in place, insert into slots in the closet flange.
  • Cock: A faucet or valve for regulating the flow of water, sometimes referred to as a ballcock.
  • Common Vent: Building drain system vertical vent which connects two or more fixture branches on the same level.
  • Compression Fitting: A kind of tubing or pipe connection where a nut, and then a sleeve or ferrule is placed over a copper or plastic tube and is compressed tightly around the tube as the nut is tightened, forming a positive grip and seal without soldering. Also a flexible connector that has a nut and gasket designed to attach directly to an SAE standard compression thread, without the use of a sleeve or ferrule.
  • Compression Valve: A type of valve that is often used for water faucets. It is opened or closed by raising or lowering a horizontal disk by a threaded stem.
  • CPVC: Chlorinated Polyvinyl Chloride - Rigid plastic pipe used in water supply systems, where code permits.
  • Culvert: A pipe-like construction of concrete that passes under a road to allow drainage.


  • Degree Rise: Difference (Delta "T") between the starting water temperature and the ending temperature after heating is complete.
  • Desanco Fitting: A type of compression adapter that connects tubular brass fittings to PVC pipe.
  • Diaphragm: Flexible membrane in a valve that deflects down onto a rigid area of the valve body to regulate water flow from the supply lines. This eliminates the possibility of debris build-up within the valve.
  • Dielectric: A nonconductor of direct electric current.
  • Dip Tube: Tube inside the water heater that sends cold water to the bottom of the tank.
  • Discharge Tube: Outlet tube that connects a disposer or sump pump to the drain line.
  • Dishwasher Tailpiece: A flanged adapter connecting a basket strainer to the drainpipe with a dishwasher inlet.
  • Diverter: Valves which direct water to various outlets. They are used in showers, tubs, bidets, and sinks.
  • Drain Valve: Device designed to allow drainage of stored contents from a water heater.
  • Dual Element Heater: An electric water heater with an upper and lower element for heating water.
  • DWV: Drainage, Waste, and Vent - A name for copper or plastic tubing used for drain, waste, or venting pipes.


  • ECO: Energy Cut Off - Safety device designed to shut power off to the water heater and prevent high temperature.
  • EF: Energy Factor - A measure of the overall efficiency rating of the water heater based on the model's recovery, efficiency, stand-by loss and energy input.
  • Efficiency: A measure of a product's ability to utilize input energy; expressed as a percentage.
  • Elbow: A pipe fitting with two openings that changes the direction of the line; also called an ell. It comes in a variety of angles, from 22 1/2° to 90°.
  • Energy Guide Label: The Federal Trade Commission (FTC) requires that gas, electric and oil residential automatic storage water heaters be labeled to show an estimated annual cost of operation for that particular model, based on a national average cost of fuel specified by FTC, as well as how the efficiency of that model compares to all other comparable models.
  • Escutcheon: A decorative metal flange or trim shield beneath a faucet handle that covers the faucet stem and the hole in the fixture or wall.
  • Expansion Tank: A tank designed to absorb excess pressure due to thermal expansion (e.g. closed system).


  • Fall/Flow: The proper slope or pitch of a pipe for adequate drainage.
  • Female Fitting: A fitting that receives a pipe or fitting. A fitting into which another fitting is inserted.
  • First Hour Delivery (Rating): Combination of the usable stored volume of hot water in tank, plus the recovery capacity for the first hour of operation.
  • Fixture: In plumbing, the devices that provide a supply of water and/or its disposal, e.g. sinks, tubs, toilets.
  • Flapper Valve: The part on the bottom of the toilet tank that opens to allow water to flow from the tank into the bowl.
  • Float Ball: The floating ball connected to the ballcock inside the tank that rises or falls with changing water levels in the tank, and actuates or shuts off the ballcock as needed.
  • Floor Flange: A fitting that connects a toilet to a floor drain.
  • Flow Control Valve: Device designed to reduce water flow (GPM) to a plumbing fixture (i.e. shower head at 5 GPM vs. 2.5 GPM); the use of flow control valves can be cost effective in load calculations, reducing the water usage and the amount of energy used to heat water.
  • Flow Rate: Rating in gallons per minute (GPM) or gallons per hour (GPH).
  • Flue: A passage way for products of combustion.
  • Flue Baffle: A device to deflect, check or regulate flow of combustion gases through the flue.
  • Flue Damper: Minimizes convective heat loss through venting system.
  • Flushometer: Toilet valve that automatically shuts off after it meters a certain amount of water flow.
  • Flushometer Tank System: Toilet flushing system that uses supply water pressure to compress water to provide a pressurized flush as opposed to a gravity flush.
  • Flux: Paste applied to copper pipes and fittings before soldering to help the fusion process and prevent oxidation.
  • Foam Insulation: The insulation surrounding the surface of the water heater tank.
  • French Drain: A covered ditch containing a layer of fitted or loose stone or other pervious material.


  • Galvanic Action: If two unlike metals are immersed in an electrolyte, an electrical potential will exist between them; if the two are in electrical contact, an electrical current will flow; the metal which becomes the anode of this cell will corrode and dissolve while the cathode will be protected from corrosion.
  • Gate Diverter: The pop-up lever on a tub faucet that activates the diverter valve.
  • Gate Valve: A device that controls the flow in a conduit, pipe, or tunnel.
  • Grain Capacity: The amount of resin, generally measured in cubic feet or 1,000 unit increments. 30,000 grains = 1 cubic ft.
  • Gravity Operated Toilet: A toilet that relies on the natural downward pressure of water in a toilet tank to flush the toilet effectively.
  • Gray Water: Waste water from sinks, showers, and bathtubs, but not toilets.


  • Head Loss: The pressure of water as measured at a stated point; it may be measured in feet or in pounds per square inch (PSI).
  • Heat Trap: Restricts heat loss through water connections to a tank.
  • Horizontal Branch: Lateral drain pipes that run from plumbing fixtures to the waste stack in a building or in the soil.
  • Horizontal Run: The horizontal distance between the point where fluid enters a pipe and the point at which it leaves.
  • Hose Bibb: An outdoor faucet, also used to supply washing machines.
  • House Trap: U-shaped fitting with two adjacent cleanout plugs visible at floor level if main drain runs under floor.
  • Hubless (No-Hub): Cast iron drainage pipe with neoprene gaskets and clamps.
  • Hydronic: System of forced hot water.
  • Hydrostatic Test: Test using non-compressible liquid under pressure at a level equal to or greater than the maximum pressure that will be utilized when in use, such as in steam boilers.


  • ID: Inside Diameter - All pipes are sized according to their inside diameter.
  • Indirect Wastes: Waste pipe used to convey gray water by discharging it into a plumbing fixture such as a floor drain.
  • Instantaneous Water Heater: A type of water heater that heats water as it flows through a heat exchanger coil.


  • Jet: An orifice or other feature of a toilet that is designed to direct water into the trapway quickly to start the siphon action.
  • Johnni-bolts: Closet bolts, used to mount toilet bowls to the closet flange.
  • Junction Box: Utility area where incoming power supply is connected to a water heater.


  • Kafer Fitting: Cast iron drainage pipe fitting with threaded-on hub used to attach to existing cast iron lines.
  • Knockout Plug: PVC test plug.


  • Lavatory (Lav): A fixed bowl or basin with running water and drainage for washing. Also referred to as a restroom or a bathroom.
  • Leach Field: Porous soil area, through which septic tank leach lines run, emptying the treated waste.
  • Leader: Pipe carrying rainwater to the ground or sewer.
  • Lock Nut: Nut fitted into a piece of pipe and screwed onto another pipe to join the two pieces.


  • Main: The primary artery of supply of the water supply or drain system in which all the branches connect. In the case of drains, known as the Main Vent.
  • Male Threads: Threads on the outside of pipes and fittings.
  • Malleable Fittings: Fittings made of metal which is soft and pliable.
  • Manifold: A fitting that connects a number of branches to the main; serves as a distribution point.
  • Micron Rating: The term applied to a filter or filter medium to indicate the particle size above which all suspended solids will be removed, throughout the rated capacity. As used in industry standards, this is an "absolute", not "nominal" rating.
  • Mixing Valve: Mixes cold water with hot water from the water heater to achieve a specified delivery temperature.
  • Multi-Stage Pump: A pump that has more than one impeller.


  • Natural Gas: A fuel delivered by a utility distribution system used on gas-fired water heaters.
  • Net Usable BTU: That portion of a fuel's heat energy actually transferred into the water by the heater.
  • Nipple: A short length of pipe installed between couplings or other fittings.
  • No-Hub Connector: A connector for no-hub iron pipe consisting of a rubber sleeve and a stainless steel band secured by hose clamps. A variation, a neoprene sleeve with two adjustable steel bands, is used for connecting dissimilar materials, as when connecting new plastic pipe to an existing cast-iron drainpipe.


  • O-Ring: Round rubber washer used to create a watertight seal, primarily around valve stems.
  • OD: Outside Diameter
  • Oakum: Loosely woven hemp rope that has been treated with oil or other waterproofing agent; it is used to caulk joints in a bell and spigot pipe and fittings.
  • One-Piece Toilet: A toilet in which the tank and bowl are manufactured as a single vitreous china fixture. One-piece toilets usually have a lower profile than two-piece toilets.
  • Operating Cost: The cost of running a water heater for a given time period.
  • Outlet Sewer: Pipe section in a septic system which runs between the septic tank and the drainage field.


  • Packing: Fibrous material that is used on faucets to prevent leaks.
  • Packing Nut: Nut that holds the stem of a faucet in position & holds the packing material.
  • Parts Per Million (ppm): A common basis for reporting the results of water and wastewater analysis, indicating the number of parts by weight of water or other solvent. In dilute water solutions, one part per million is practically equal to one milligram per liter, which is the preferred unit. 17.1 ppm equals one grain per US gallon. One ppm equals one pound per million pounds of water.
  • PB: Polybutylene - Flexible plastic tubing used in water supply systems where allowed by code.
  • Peak Hour Demand: Time when the largest demand for hot water is needed.
  • Peak Load Period: That period of the day when the system has the greatest demand.
  • pH: Potential Hydrogen - The hydrogen ion concentration of water to denote acidity or alkalinity, measured on a scale of 0 to 14. Below 7 denotes acidity; above 7 denotes alkalinity.
  • Pilot: A small burner used to ignite the main burner.
  • Pipe Dope: Slang for pipe-joint compound. Substance applied to threaded fittings to create a watertight seal.
  • Pitch: Downward slope of a drain pipe in the direction of the water flow.
  • Plumb: Precisely vertical. Also to test for, or to make vertical. Also to perform plumbing work.
  • Plumber's Putty: Pliable putty used to seal joints between drain pieces and fixture surfaces.
  • Plumbing Tree: Prefabricated set of drain waste, vent, and supply lines.
  • Plunger: An instrument usually with a rubber head, used to create suction in a drain line or a toilet to push a clog through the line.
  • Point Of Use Water Heater: Small water heater used for remote locations.
  • Pop-Up Drain: Type of drain assembly for lavatory and bath. When a lavatory lift rod or bath overflow plate lever is lifted, the pop-up drain closes so the lavatory or tub retains water.
  • Port: An opening in a burner head through which gas or an air-gas mixture is discharged for ignition.
  • Positive Displacement Pump: Called a PD pump. Gear, sliding vane, progressive cavity, lobe etc. the capacity determined by the pump speed. The maximum head is determined by the horsepower available and the casing strength.
  • Pressure Balance Valve: Shower mixing valve that automatically maintains balance between incoming hot and cold water supplies by immediately regulating fluctuations in pressure. As a result, temperature remains constant, though the outlet pressure may drop. Also known as an anti-scald valve.
  • Pressure Reducing Valve: A valve that automatically reduces inlet water pressure to a specified value at its outlet under static cold water conditions.
  • Pressure Tank: Device used to pump water from a well.
  • Pressure Tubing: Tubing used to conduct fluids under pressure or at elevated temperatures or both, and produced to stricter tolerances than pipe.
  • PVC: Polyvinyl Chloride - A rigid white or cream-colored plastic pipe used in non-pressure systems, such as drainage, waste, and vent systems.


  • Quick Connect: A fitting that is designed to attach to a line quickly and efficiently. A quick connect fitting is often a one-piece fitting that is forced onto the end of a hose and locked into place.


  • Rated Storage Volume: Quantity of water (expressed in gallons) stored in a tank.
  • Reamer: A grinding tool used to level or remove burrs from valve seats in faucets so that the valve stem will fit properly.
  • Recovery (GPH): The amount of water in gallons that can be heated in one hour.
  • Reducer: A fitting that connects pipes of different sizes together.
  • Reserve Capacity: The amount of grain capacity allowed as a reserve to ensure softened water until the delayed regeneration time occurs.
  • Return Circulation System: Tempered water from or near the point of usage which eliminates waste of hot water used for long runs and adds storage to the system.
  • Revent: Pipe installed specifically to vent a fixture trap. Connects with the vent system above the fixture.
  • Reverse Osmosis: A water treatment method whereby water is forced through a semi permeable membrane which filters out impurities.
  • Reverse Trap Water Closet: A water closet having a siphonic trapway at the rear of the bowl, and integral flushing rim and jet.
  • RF: Recovery Factor - Rating based on the efficiency of the product which is input required to raise 1 gallon of water 1°F.
  • Rigid Pipe: Pipe designed to transmit the backfill load to the foundation beneath the pipe. Rigid pipe must be supported on the bottom portion of the pipe.
  • Rim Holes: A series of small holes in the underside of a toilet rim, around the circumference of the bowl. Incoming water flows down into the bowl through these holes, creating a rinse effect or wash over the entire inner surface of the bowl.
  • Riser: A vertical metal or plastic tube or assembly that connects a faucet to the water supply stop valve. Usually made of copper. Metal Flex Risers are corrugated to facilitate bending. Also a supply line that rises from one story to the next.
  • Rough-In: Installation of the drain, waste, vent, and supply lines in a structure to the proposed location of each fixture.
  • Rough-In Dimensions: The distance from a finished wall or floor to the center of the waste or supply opening or mounting holes on a plumbing fixture.
  • Run: A complete or secondary section of pipe that extends from supply to fixture or drain to stack.


  • Saddle Valve: A valve mounted on a pipe run by a clamping device, or fitting that taps into the side of a pipe, used to make quick connection to an existing line to provide a water supply for a low-demand device.
  • Safety Shut Off Valve: A device on a gas appliance which shuts off the gas supply to prevent a hazardous situation. A flame failure safety shut off operates when the actuating flame becomes extinguished. A 100% shut off cuts off all gas including main and pilot burners.
  • Sanitary Fitting: Fitting that joins the assorted pipes in a drain, waste and vent system; designed to allow solid material to pass through without clogging.
  • Sanitary Sewer: House drain that carries wastewater away from the house to a sewer system or septic tank.
  • Self-Rimming Sink: Sink with no metal ring that has a built-in lip of the same material which supports it in the vanity top.
  • Shroud: Color-matched component under a wall-mount lavatory that covers the drain outlet for aesthetic purposes.
  • Siphon-Vortex Water Closet: A toilet having a trapway at the rear of the bowl, integral flushing rim, and a water supply system with or without a jet, which does not feed directly into the trap.
  • Sleeve: Pipe which is passed through a wall for the purpose of inserting another pipe through it.
  • Slip Joint: A connection made with compression fittings.
  • Soil Stack: Largest vertical drain line to which all branch waste lines connect. This line carries waste to the sewer line.
  • Solder: Metal alloy that is melted to create a fused joint between metal pieces. Also the act of melting solder into the joint.
  • Stack: The vertical main in the drain, waste, and vent system, extending one or more stories.
  • Stand Pipe: Open vertical pipe that receives water from a washing machine. Also the vertical pipe run supplying water to a fire sprinkler system; also large vertical pipe into which water is pumped in order to produce a desired pressure; a high vertical pipe or reservoir that is used to secure a uniform pressure in a water-supply system.
  • Static Lift: The vertical distance between source and discharge water levels in a pump installation.
  • Stop Valve: The shutoff valve under sinks and toilets. Allows water supply to be cut off to one fixture without affecting the water supply to other fixtures.
  • Straight Cross: Fitting that connects four pipes of the same diameter.
  • Sump: A pit or pool for draining, collecting, or storing water. A chamber which provides water to the pump.
  • Sweating: Slang term for soldering. Also formation of condensation on the outside of pipes or toilet tanks.


  • T & P Valve: Temperature & Pressure Relief Valve. A safety device used to expel excess pressure or temperature from inside a tank.
  • Tail Pipe: The pipe added below the jet assembly, in a weak well application.
  • Tailpiece: Section of pipe that runs between a fixture outlet and the trap.
  • Tank: Fixture reservoir for flush water. On a conventional toilet, the ballcock, flush valve, and trip lever are installed in the tank. A tank lid closes the top tank opening.
  • Tank Cross: A double-tee-shaped fitting installed between a shallow well pump and the bladder tank with integrated valve and gauge fittings, and an outlet for a pressure-relief valve.
  • Tankless Water Heater: Commonly known as instantaneous or point-of-use water heaters, where water is heated on an as needed basis.
  • Tap Tee: Cast iron tee with a threaded female side inlet.
  • Tee: A T-shaped fitting with three openings used to create branch lines.
  • Temperature Rise: (Delta "T") The number of degrees Fahrenheit (F) the incoming cold water must be raised to reach the desired hot water temperature.
  • Thermal Expansion: Water, a non-compressible liquid, expands when heated.
  • Thermocouple: Small electric generator. Electron flow between the hot junction of 1200 degrees F and cold junction of 600 degrees F creates millivoltage.
  • Thermostatic Valve: Pressure-balancing shower mixing valve with automatic temperature control. When temperature or pressure fluctuations occur at the water inlets, a thermal actuator adjusts the hot and cold ratio to maintain the original temperature setting.
  • Trap: Curved section of drain line that prevents sewer odors from escaping into the atmosphere. All fixtures that have drains must have a "P" trap installed. A toilet is the only plumbing fixture with an "S" trap.
  • Trap Arm: The waste arm portion of a drainage trap.
  • Trap Dip: The U-bend portion of a drainage trap.
  • Trap Primer: A small feeder line connecting the cold water line directly to the drainage trap, which releases a small amount of water to the trap should it run dry to maintain the water seal.
  • Trap Seal: Height of water in a toilet bowl "at rest.". It provides the water seal which prevents sewer gases from entering the home. It is measured from the top of the dam down to the inlet of the trapway. Also referred to as deep seal.
  • Trapway: Channel in a toilet that connects the bowl to the waste outlet. It is where the siphonic action takes place. The trapway is measured in terms of the largest diameter ball which can pass through it. Also called the passageway.
  • Trip Lever: Flush handle and actuating arm on a toilet tank. Also the lever that opens and closes the drain on the bathtub waste and overflow.
  • Turbulent Flow: A fluid flow in which the velocity at a given point varies erratically in magnitude and direction.


  • UL: Underwriters Laboratories.
  • Uni-flex: One piece stop and riser combination. One-piece supply.
  • Union: Three piece fitting that joins two sections of pipe, but allows them to be disconnected without cutting the pipe. Used primarily with steel pipe; never in a DWV system.
  • Usable Storage: Percentage of hot water that can be drawn from a tank before the temperature drops to a point that it is no longer considered hot.


  • Vacuum Breaker: An anti-siphon device that prevents the backflow of contaminated water into the water supply system.
  • Vacuum Relief Valve (Anti-Siphon): Recommended for installation on all side (bottom) cold inlet heaters; prevents internal vacuum conditions that could drain a system by back siphonage, eliminates burned out electric elements and collapsed tanks.
  • Valve Seat: The non-moving part of a valve. Water flow is stopped when the moveable portion of the valve comes in contact with the valve seat.
  • Vent: A pipe that allows air into a drain system to balance the air pressure, preventing water in the traps from being siphoned off.
  • Vent Header: A vent pipe into which several vents connect. The vent pipe leads to the vent stack and out of the building.
  • Vent Stack: Upper portion of the soil stack above the topmost fixture through which gases and odors escape.
  • Vent System: A vent is a pipe or pipes instalto provide a flow or air to or from a drainage system to provide a circulation of air within such system to protect trap seals from siphonage and back-pressure.
  • Venturi: A short tube with a tapered constriction in the middle that causes an increase in the velocity of flow of a fluid and a corresponding decrease in fluid pressure and that is used for creating a suction in a vacuum pump.
  • Viscosity: The resistance of fluids to flow, due to internal forces and friction between molecules, which increases as its temperature decreases.
  • Vitreous China: Ceramic materials fired at high temperature to form a non-porous body, having exposed surfaces coated with ceramic glaze fused to the body. This is used to form bathroom fixtures such as toilets, bidets, and lavatories.


  • Washdown Water Closet: Water closet having a siphon trapway at the front of the bowl, and integral flushing rim.
  • Waste Arm: Drain extension pipe, usually to extend a sink drain into a wall.
  • Waste & Overflow: Drain assembly for a bathtub. The outlet at the top removes the overflow water during tub filling and the drain at the bottom removes wastewater when the tub is drained.
  • Water Consumption: The use of water in the home, calculated in U.S. gallon increments. It is most efficient to determine this figure by obtaining the average water consumption figures on past copies of water department billing statements. If this is not possible, allow for 75 gallons per day average per person, and 75 gallons per day for automatic washer/dishwasher combined.
  • Water Hardness: The amount of calcium and magnesium carbonate and sulphide, measured in grains per gallon or parts per million.
  • Waterway Fitting: A channel through which water can flow; connects water heater to inlet & outlet lines.
  • Wet Vent: A wet vent is a vent that also serves as a drain.
  • Widespread: A style of bathroom lavatory faucet having separate spout and handles, usually 8" from center of handle to handle.
  • WYE: A Y-shaped fitting with three openings used to create branch lines.


  • Yearly Cost: The cost of operating a water heater for a year.
  • Yoke: Usually a brass casting that holds both the hot and cold valves and the mixing chamber for the water. May also refer to an assembly of copper or other metal which serves the same function.
  • Yoke Vent: A yoke vent is a pipe connecting upward from a soil or waste stack to a vent stack for the purpose of preventing pressure changes in the stacks.
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