Plumbing glossary

Backflow

Water flowing backwards into the clean supply, for example from a hose left in a bucket or an irrigation system. Prevented by backflow preventers, which many cities require to be tested every year.

Backflow preventer

A valve assembly that stops used or contaminated water flowing back into the drinking-water supply. Testing it is a licensed specialty in many places.

Ball valve

A shut-off valve with a lever handle that opens or closes in a quarter turn. Common on main shut-offs because it is quick and reliable.

Cleanout

A capped opening in a drain or sewer line that gives a plumber access to clear a blockage without taking pipes apart.

Copper pipe

A long-lasting metal water pipe joined by soldering or press fittings. Types K, L and M differ in wall thickness.

CPVC

Chlorinated PVC: a rigid plastic pipe rated for hot and cold water supply, joined with solvent cement.

Cross-connection

Any link between drinking water and a possible source of contamination. Backflow preventers exist to control them.

Dielectric union

A fitting that joins two different metals, such as copper and steel, while keeping them apart to slow corrosion.

Drain-waste-vent (DWV)

The system of pipes that carries waste water out of a building and lets air in so drains flow freely.

Expansion tank

A small tank on the water heater line that absorbs the extra volume of water as it heats, protecting the system from pressure spikes.

Fixture

Anything that uses water and drains it: sinks, toilets, tubs, showers and similar.

Flapper

The rubber seal at the bottom of a toilet tank. A worn flapper is the usual cause of a toilet that keeps running.

Galvanized pipe

Steel pipe coated with zinc, common in older homes. It corrodes from the inside over decades, reducing pressure.

Gas line

Piping that carries natural gas or propane to appliances. Work on it is regulated and often needs a permit.

Grease trap

A device that catches fats and oils before they reach the sewer; required in most commercial kitchens.

Hose bib

An outdoor faucet. Frost-free versions keep the valve inside the warm wall to prevent freezing.

Hydro jetting

Clearing a drain or sewer line with a high-pressure stream of water, which scours the pipe walls rather than just punching a hole through a clog.

Journeyman plumber

A plumber who has finished an apprenticeship and passed a licensing exam where the state requires one, and may work without direct supervision.

Main shut-off valve

The valve that stops all water entering the building. Knowing where it is matters most in an emergency.

Master plumber

A plumber with further experience and a higher license. Many states require a master plumber to oversee a plumbing business or pull permits.

P-trap

The U-shaped bend under a sink that holds a little water to stop sewer gas coming back into the room.

PEX

Cross-linked polyethylene: flexible plastic water-supply tubing, widely used for new work and repiping.

Pressure-reducing valve (PRV)

A valve on the main line that lowers high street water pressure to a safe level for the house.

PVC

A rigid plastic pipe used mainly for drains, waste and vents.

Relief valve (T&P valve)

The temperature and pressure relief valve on a water heater. It opens to release water if the tank gets too hot or the pressure too high.

Repiping

Replacing the water-supply pipes throughout a building, usually because old pipes are corroded or leaking.

Rough-in

The stage of a build or remodel when pipes are run inside walls and floors, before fixtures are installed.

Sewer camera inspection

Running a waterproof camera through a drain or sewer line to see cracks, roots or blockages.

Sewer lateral

The pipe that runs from a building to the public sewer main. The homeowner is often responsible for part of it.

Shut-off valve

A valve that stops water to a single fixture or appliance, usually under or behind it.

Slab leak

A leak in a water line running under a concrete floor slab. Found with electronic leak detection.

Sump pump

A pump in a pit at the lowest point of a basement that pumps out groundwater before it floods.

Tankless water heater

A heater that warms water as it flows, instead of storing it in a tank. Also called on-demand.

Trap seal

The water held in a trap that blocks sewer gas. It can dry out in drains that are rarely used.

Vent stack

A vertical pipe that runs through the roof and lets air into the drain system so water drains without gurgling or siphoning traps.

Water hammer

A loud bang in the pipes when a valve closes quickly. It can be reduced with arrestors or a pressure-reducing valve.

Water softener

A unit that removes the minerals that cause hard water and scale in pipes and appliances.

Wax ring

The seal between the base of a toilet and the drain flange in the floor.

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