Reference
The Plumbing Glossary
Plain-English definitions of plumbing and trade terms — written for working professionals, not homeowners.
A
B
- Backflow PreventerA valve that stops contaminated water from flowing backward into the potable water supply.
- Backwater ValveOne-way valve installed in a drain line to prevent sewage from flowing backward into a building during main line blockage or surcharge.
- Ball ValveA valve with a rotating hollow ball inside that controls flow by aligning or blocking a port; the standard on-off shutoff for water lines.
C
- Camera InspectionVideo inspection of interior pipe conditions using a waterproof camera on a cable or crawler, transmitted to an above-ground monitor.
- CleanoutAn accessible opening in a drain line that lets you snake, jet, or inspect the pipe.
- Compression FittingA mechanical connection that seals tubing by compressing a ferrule (ring) against the fitting body when the nut is tightened.
- CSSTFlexible stainless steel tubing with a corrugated outer wall, used for gas and water lines where rigid pipe isn't practical.
D
- Dielectric UnionA coupling that joins two dissimilar metals using an insulating barrier to prevent galvanic corrosion.
- DWVThe system of pipes that removes wastewater and sewer gases from fixtures, vents them safely to atmosphere, and prevents siphoning.
E
- Ejector PumpA submersible pump that lifts sewage from a below-grade collection tank up to the main drain or septic system.
- EscutcheonA trim ring or flange that covers the gap between a pipe and a wall or floor penetration.
- Expansion TankA sealed vessel that absorbs excess pressure created when water heats and expands in a closed system.
F
G
- Gate ValveA shutoff valve with a wedge-shaped gate that slides perpendicular to flow; full-port and no-restriction when open.
H
- Hydro JettingHigh-pressure water stream (typically 3,000–4,000 psi) forced through a hose to blast debris, grease, and roots from inside pipes.
M
- ManifoldA central distribution block that branches one incoming water line into multiple controlled outlets, typically used in PEX systems.
- MIPA threaded male connection with National Pipe Thread (NPT) used to join pipes and fittings.
- Mixing ValveA valve that blends hot and cold water to deliver a preset, stable outlet temperature regardless of inlet pressure or temperature swings.
N
- No-Hub CouplingA rubber-and-stainless-steel sleeve that connects two hub-less pipes without threading or soldering.
P
R
- Recirculation PumpA pump that continuously cycles hot water through supply lines so it reaches fixtures instantly without running water down the drain.
S
- S-trapA trap bent into an S shape, now banned under code because it siphons out under normal conditions.
- SDRThe ratio of pipe outside diameter to wall thickness; determines pressure rating and cost of plastic pipe.
- SharkBiteA brass push-fit coupling that grips copper, PEX, or CPVC pipe without soldering, crimping, or clamps—just push the tubing in.
- SillcockAn outdoor water faucet that mounts through a wall, typically with a long shank to clear exterior insulation.
- Slab LeakA water leak in supply or drain lines running beneath a concrete foundation or floor slab.
- Sump PumpA submersible pump installed in a sump pit to remove groundwater and prevent basement flooding.
- Sweat FittingA copper or brass fitting joined to copper tubing by heating and running solder into the joint without a threaded connection.
T
- Tankless Water HeaterA water heater that heats water on demand as it flows through the unit, with no storage tank.
- TPR ValveA safety valve that opens when water heater temperature or pressure exceeds safe limits, dumping water to prevent tank rupture.
- Trap PrimerA device that automatically refills a trap seal with water to prevent siphonage and sewer gas entry.
U
- Union FittingA threaded coupling with a movable nut that lets you connect and disconnect two pipes without turning the pipes themselves.
V
- Vent StackThe primary vertical pipe that carries sewer gases and air to atmosphere, allowing waste to drain and traps to refill.
W
- Water HammerA sharp banging noise and pressure spike in pipes caused by sudden water flow stoppage, usually at a valve or fixture.