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This Glossary of Terms is intended for use in context with this website. Other definitions for these terms may also be relevant when used in a different context. The plumbing terms are courtesy of PBS.

Plumbing Terms and Definitions


Acrylonitrile-butadiene-styrene. Used for drain and vent lines.


The system of screens screwed into the spout of most faucets. The aerator helps control the flow of water and keep it from splashing all over. They frequently contain a baffle to help reduce the flow of water to the mandated 2.5 gallons per minute.

Air Admittance Valve (AAV)

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.


In the drainage system, the unobstructed vertical opening between the lowest opening of a waste line and the flood level of the device into which it empties. Purpose is to prevent backflow contamination.

Anti-scald Valve

See Pressure-balancing Valve

Backflow Preventer

A device that prevents wastewater and other contaminants from flowing into the potable water supply. Generally required for sprinkler systems, hand-held showers installed in bathtubs, faucets with pullout spouts, kitchen sprayers, and the like.


A valve operated by a float, such as a floatball or a float-cup in a toilet tank.


Any part of the drain system other than the main, riser, or stack.


A pipe fitting used to join two pipes of different sizes. A bushing is threaded inside and out.

Check Valve

A type of backflow preventer installed in a pipe run that allows water to flow in only one direction.


A pipe fitting with a removable plug for inspecting and cleaning out drain pipes.

Closet Bend

The curved section of drain pipe located immediately below the toilet.

Closet Flange

A round, flat fitting that attaches to the closet bend. The heads of closet bolts, used to secure the toilet in place, insert into slots in the closet flange.


A short fitting used to join two pieces of pipe.


Chlorinated polyvinyl chloride. Used for water supply.


Any connection or situation that may allow waste water to enter the supply system.


Any pipe that carries wastewater or water-borne waste.


Drainage, waste, and vent.


Curved fittings, usually 90 degree or 45 degree, used to change the direction of a pipe run. Also called “ells.”


A decorative or protective plate. In plumbing, the plate behind or under a fixture that covers the hole around the pipe or valve.


Any pipe part used to join together two sections of pipe, such as elbows, couplings, bends, wyes, etc.


Accepts or discharges water or wastewater, such as faucets, sinks, toilets, etc.

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

In the toilet tank, the hollow ball attached to a rod that rises as the tank refills and shuts the water inlet valve.


Substance applied to copper pipes and fittings before soldering to help the fusion process and prevent oxidation.


Device used to support pipes.

Hose Bibb

An outdoor faucet, also used to supply washing machines.


Industry term for bathroom sink.


The primary artery of the supply or drain system to which all the branches connect. Referred to as the Main Vent in the vent system.


A fitting that connects a number of branches to the main; serves as a distribution point.


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 drain pipe.


The packing material used before sealing a hubbed cast-iron fitting with lead.


Cross-linked polyethylene. PEX tubing, commonly used for hydronic radiant floor heat, is increasingly used for water supply lines.

Pipe Dope

Slang for pipe-joint compound. Substance applied to threaded fittings to create a watertight seal.


Water that suitable for consumption.

Pressure-balancing Valve

A mixing valve that monitors the water pressure in both the hot and cold supply lines and compensates for a drop in either one.


Polyvinyl chloride. Used for drain and vent lines.


A fitting that allows pipes of different sizes to be joined together.

Relief Valve

A valve that opens to relieve excess temperature and/or pressure in the system. See T&P Valve.


A supply line pipe that rises from one story to the next; also the short vertical pipes that bring water from the branch to the fixture.


Installation of the drain, vent, and supply lines in the structure prior to installation of the fixtures.

Shutoff Valve

Most commonly refers to the angle stops installed under sinks and toilets, but valves are also installed on branch lines and alongside the meter.


Another name for hose bibb.


A metal alloy that is melted to create a fused joint between metal pieces.


The vertical main in the DWV system extending one or more stories.


The shutoff valves under sinks and toilets.


Short lengths of pipe installed during rough-in to which fixtures and drains will eventually be installed.


Slang for soldering.


The eased change of direction in a drain fitting that allows for smooth passage of waste. Fittings with abrupt changes of direction, such as a vent tee, may only be used for vents.

T&P Valve

Temperature and pressure valve. A valve that opens to release excess pressure and temperature in a system.


The section of pipe that runs between a fixture outlet and the trap.

Tee Fitting

Fittings that allow another pipe to be joined at a 90-degree angle. Those for the drain system have the changes of direction eased. See Sweep.


A fitting or portion of a fixture that, when properly vented, holds water to prevent entry of sewer gases.


A device that regulated the flow of water.

Valve Seat

The immovable portion of a valve. Water flow is stopped when the movable portion of the valve comes in contact with the valve seat.


A pipe that allows air into a drain system to balance the air pressure, preventing the water in the traps from being siphoned off.

Water Hammer Arrestor

A device installed near a fixture to absorb the hydraulic shock that happens when a fixture’s supply is suddenly shut off, causing water hammer, a loud banging noise in the pipes.

Wye Fitting

A drain fitting that allows one pipe to be joined to another at a 45-degree angle.