Plain-language reference
Plumbing terms, defined plainly
119 terms covering tools, pipe anatomy, failure modes, trenchless methods, and water heating — written by the AlertPlumber editorial team and cited to IAPMO, EPA, and NOAA.
119 Terms defined
18 A–Z sections
100% Fully written entries
A (4)
- ABS Pipe (Acrylonitrile Butadiene Styrene) Black rigid plastic pipe for drain, waste, and vent service; one-step cement; common in Western U.S. residential.
- Air Admittance Valve One-way mechanical vent that lets air into a drain line to prevent trap siphoning, used where running a vent through the roof i…
- Angle Stop A small shutoff valve under sinks and behind toilets that isolates a single fixture from the water supply without shutting off …
- Anode Rod Sacrificial magnesium or aluminum rod inside a water heater tank that corrodes in place of the steel tank lining.
B (6)
- Backflow Preventer Valve assembly that prevents non-potable water from being siphoned or pushed back into the potable supply.
- Backwater Valve A one-way check valve installed on a basement drain line that automatically closes to prevent sewage from backing up into the h…
- Ball Valve A quarter-turn valve with a spherical disc that controls flow. Turning the lever 90 degrees fully opens or closes it — the most…
- Bidet A plumbing fixture or toilet seat attachment that uses a stream of water for personal hygiene after using the toilet — increasi…
- Boiler A closed vessel that heats water for residential or commercial space heating via hot water (hydronic) or steam distribution sys…
- Burst Pipe A pipe that has ruptured due to pressure — most commonly from freezing, corrosion, or physical damage — releasing water that ca…
C (9)
- Cast Iron Pipe Heavy iron drain, waste, and vent piping used in homes built before 1980, with 75 to 100 year typical lifespan.
- Check Valve A one-way valve that allows water or gas to flow in only one direction and automatically closes to prevent reverse flow — used …
- CIPP (Cured-In-Place Pipe) Trenchless sewer-lining technology that installs an epoxy-saturated felt liner inside an existing damaged pipe and cures it in …
- Cleanout Capped Y-fitting on a drain line that provides access for snake or hydro-jet equipment; required at code-defined intervals.
- Clog A partial or complete blockage inside a drain pipe that restricts or stops water flow. Clogs are caused by buildup of hair, gre…
- Closet Auger A specialized drain snake designed specifically for toilets, with a protective sleeve that fits into the bowl without scratchin…
- Compression Fitting A plumbing connector that joins pipes without soldering — a compression nut and ferrule (ring) compress against the pipe to cre…
- Copper Pipe The most widely used metal pipe for residential water supply lines. Durable, corrosion-resistant, and antimicrobial — copper ha…
- CPVC (Chlorinated Polyvinyl Chloride) Cream-tan rigid plastic pipe rated for hot and cold potable water; brittle in cold and UV; 50-75 year service life.
D (5)
- Dielectric Union Fitting that joins dissimilar metals like copper to galvanized steel, with insulating gasket to prevent galvanic corrosion.
- Dip Tube Plastic tube inside a water heater that delivers incoming cold water to the bottom of the tank for heating.
- Diverter Valve A valve that redirects water flow from one outlet to another — most commonly from a tub spout to a showerhead, or between multi…
- Drain Snake (Plumbing Auger) A flexible metal cable with a corkscrew or blade tip used to break up or retrieve clogs in drain pipes. Available in hand-crank…
- Drum Trap An older cylindrical trap design — a large metal can-shaped trap used under bathtubs and floor drains from the early 1900s thro…
F (6)
- Faucet Aerator The small screen screwed onto the tip of a faucet spout that mixes air into the water stream — reducing flow rate, preventing s…
- Faucet Cartridge The internal valve mechanism inside a cartridge faucet that controls water flow and temperature. Replacing a worn cartridge fix…
- Floor Drain A drain set flush with the floor in basements, laundry rooms, garages, and utility areas that removes overflow water, equipment…
- Flux A paste applied to copper pipe and fittings before soldering to clean the metal surface and help solder flow evenly into the jo…
- Frost Line The maximum depth at which the ground freezes in a given climate. Water service lines, sewer laterals, and outdoor plumbing mus…
- Frozen Pipe A water pipe in which the water inside has frozen solid, blocking flow and risking a rupture. Frozen pipes are the leading caus…
G (6)
- Galvanized Pipe Zinc-coated steel water supply pipe used from the 1880s to the 1960s, prone to interior rust and lead leaching.
- Garbage Disposal An electrically powered device installed under the kitchen sink that grinds food waste into small particles that can pass throu…
- Gas Line The piping that carries natural gas or propane from the utility meter or tank to appliances like water heaters, furnaces, stove…
- Gas Shutoff Valve The valve that controls gas flow to an individual appliance or to the entire building. Knowing its location is critical for saf…
- Gate Valve A multi-turn shutoff valve that uses a rising wedge gate to stop flow. Common in older homes but increasingly replaced by ball …
- Grease Trap A plumbing device that intercepts fats, oils, and grease before they enter the sewer system — required by code in commercial ki…
H (4)
- Heat Tape Electrically heated cable wrapped around vulnerable pipes to prevent freezing in unheated spaces. Essential for pipes in exteri…
- Hose Bib Outdoor faucet on a buildings exterior wall used for garden hoses; freeze-prone unless installed as a frost-free model.
- Hot Water Recirculation A system that keeps hot water continuously circulating through supply lines so it arrives instantly at fixtures — eliminating t…
- Hydro Jetting A drain-cleaning method using a high-pressure water stream (2,000–4,000 PSI) delivered through a specialized nozzle to scour pi…
M (3)
- Main Shutoff Valve The valve that controls all water flow into a building. Closing it immediately stops water to every fixture — essential during …
- Manifold A central distribution hub where a single main supply line branches into multiple individual lines, each with its own shutoff —…
- Mixing Valve A valve that blends hot and cold water to a set output temperature — used on water heaters, showers, and point-of-use applicati…
P (23)
- P-Trap Curved pipe under sinks, tubs, and showers that holds a pool of water to block sewer gas from entering the home.
- PEX (Cross-Linked Polyethylene) Flexible plastic plumbing pipe that has largely replaced copper and galvanized steel in residential supply lines since 2000. Le…
- Pilot Light A small, continuously burning gas flame inside a water heater or furnace that ignites the main burner when heat is needed.
- Pipe Bursting Trenchless pipe-replacement method that pulls a new pipe through the existing one while a bursting head fragments the old pipe …
- Pipe Cutter A hand tool that cuts copper, CPVC, or PEX pipe with a clean, square edge using a rotating cutting wheel rather than a saw — es…
- Pipe Dope A paste-form thread sealant applied to threaded pipe joints to prevent leaks. Also called pipe joint compound — used on metal t…
- Pipe Insulation Foam, fiberglass, or rubber sleeve wrapped around pipes to prevent freezing in cold weather, reduce heat loss from hot water li…
- Pipe Joint Any connection point between two sections of pipe or between a pipe and a fitting. The quality of pipe joints determines a plum…
- Pipe Scale Mineral deposits (primarily calcium carbonate) that accumulate on the interior walls of pipes and water heaters in hard-water a…
- Plumb Bob A weight suspended on a string used to establish a true vertical reference line. Essential for aligning drain stacks, pipes, an…
- Plumber's Putty A soft, pliable sealing compound used to create watertight seals around sink drains, faucet bases, and strainers. Not suitable …
- Plumber's Tape (PTFE Tape) Thin polytetrafluoroethylene (PTFE) tape wrapped around threaded pipe connections to create a leak-free seal. Also called Teflo…
- Plumbing Code The body of regulations governing how plumbing systems must be designed, installed, and maintained — adopted at the state or lo…
- Plumbing Fittings Connectors used to join, redirect, or terminate pipes in a plumbing system. Types include couplings, elbows, tees, reducers, an…
- Plumbing Vent (Vent Stack) Pipes that connect the drain-waste system to outdoor air, preventing siphoning of P-trap water seals and allowing sewer gases t…
- Plunger A hand tool that uses suction and hydraulic pressure to dislodge drain clogs. The cup plunger works on sinks and tubs; the flan…
- Polybutylene (PB) Gray or blue plastic supply pipe used 1978-1995; failure-prone after 10-15 years; insurance often denies coverage.
- Pop-Up Drain The drain assembly in bathroom sinks with a stopper that moves up and down via a pivot rod connected to the faucet lift rod — a…
- Pressure Balance Valve A shower valve that automatically adjusts the hot/cold ratio to maintain temperature within ±3°F when pressure fluctuations occ…
- Pressure Reducing Valve (PRV) Spring-loaded valve that drops incoming municipal water pressure to a safe and code-compliant level for the home.
- Pressure Tank A tank in a well water system that stores pressurized water and maintains consistent pressure between pump cycles — preventing …
- Push-Fit Fitting Quick-connect plumbing fitting that joins copper, PEX, or CPVC pipe by pushing pipe into the body without solder, crimp, or glue.
- PVC Pipe (Polyvinyl Chloride) White rigid plastic pipe for drain, waste, vent, and cold supply only; never approved for hot potable water.
R (5)
- Repipe (Whole-House Repipe) Complete replacement of a home's interior supply lines — typically switching from failing galvanized steel or polybutylene to P…
- Reverse Osmosis A water purification process that forces water through a semi-permeable membrane to remove dissolved solids, contaminants, and …
- Riser A vertical pipe in a plumbing system — either a supply riser carrying water upward to upper floors and fixtures, or a drain ris…
- Rooter A motorized drain cleaning machine that uses a spinning steel cable with a cutting attachment to break up and remove clogs, tre…
- Rough-In Plumbing The first phase of plumbing installation where supply lines, drain pipes, and vent stacks are run through walls and floors befo…
S (19)
- Sanitary Tee A drain-waste-vent fitting shaped like a letter T with a curved sweep on the branch inlet, designed to connect branch drains to…
- Sediment Filter A whole-house or point-of-use filter that removes particles (sand, rust, silt) from water supply lines — the first line of defe…
- Sewage Pump A submersible pump that moves raw sewage from a collection pit to a higher elevation where it can drain by gravity — used when …
- Sewer Camera Inspection A waterproof video camera on a flexible cable fed through a sewer lateral or drain to visually inspect pipe condition, locate c…
- Sewer Gas A toxic mixture of gases produced by decomposing waste in sewer lines — including hydrogen sulfide, methane, and ammonia — that…
- Sewer Lateral Underground pipe carrying wastewater from the house to the city sewer main; ownership boundary varies by municipality.
- SharkBite Fitting A brand of push-fit plumbing connector that joins copper, PEX, CPVC, or PE-RT pipes without soldering, crimping, or gluing. Int…
- Shower Drain The drain assembly in the shower floor that collects water and directs it through the P-trap into the drain line. Available in …
- Shower Pan The waterproofed floor of a shower that collects water and directs it to the drain. Shower pan failures cause water damage insi…
- Shower Valve The mixing valve behind the shower wall that blends hot and cold water to the set temperature and controls flow to the showerhe…
- Shutoff Valve Manual valve that isolates water flow to a fixture, branch, or the entire building; required at the building entry and at every…
- Silicone Sealant A flexible, waterproof sealant used around tubs, showers, sinks, and fixtures to prevent water infiltration at joints between p…
- Sink Strainer The drain fitting at the bottom of a kitchen sink that catches food particles and debris while allowing water to drain — connec…
- Slab Leak A water leak in copper supply lines running through or beneath a home's concrete slab foundation. Common in Sun Belt homes buil…
- Slip Coupling A coupling fitting with no internal stop that can slide fully over a pipe, allowing it to be positioned over a repaired section…
- Standpipe A vertical pipe that provides an indirect drain connection for washing machines and other appliances — preventing dirty water f…
- Sump Pump Submersible or pedestal pump installed in a basement floor pit that ejects groundwater to prevent flooding.
- Supply Line The flexible hose that connects a shutoff valve (angle stop) to a faucet, toilet, or appliance. Supply lines are a common sourc…
- Sweating Pipes Condensation on cold-water pipes in humid spaces; looks like a leak but is moisture from the air collecting on the cold pipe su…
T (9)
- T&P Valve (Temperature & Pressure Relief) Code-required safety valve on water heaters that opens if temperature exceeds 210F or pressure exceeds 150 psi.
- Tankless Water Heater An on-demand water heater that heats water directly as it flows through the unit, with no storage tank — delivering hot water o…
- Thermocouple A safety device in gas water heaters and furnaces that detects whether the pilot light is burning and shuts off gas flow if the…
- Toilet Fill Valve The mechanism inside the toilet tank that controls water refilling after a flush. A faulty fill valve causes running toilets, s…
- Toilet Flapper The rubber seal at the bottom of the toilet tank that opens to flush and closes to refill. A worn flapper is the #1 cause of a …
- Toilet Rough-In The distance from the finished wall behind the toilet to the center of the toilet drain. The standard rough-in is 12 inches — b…
- Trap Primer A device that automatically adds small amounts of water to infrequently used floor drain P-traps to prevent the water seal from…
- Trenchless Sewer Repair Methods for repairing or replacing underground sewer pipes with minimal excavation. The two main methods are CIPP lining (pipe-…
- Tub Drain The drain fitting at the bottom of a bathtub that connects to the P-trap and drainpipe. Includes the stopper mechanism that hol…
W (12)
- Water Hammer Loud banging or thudding noise in pipes when a valve closes suddenly, caused by a pressure shockwave hitting the pipe wall.
- Water Hardness A measure of dissolved calcium and magnesium in water, expressed in grains per gallon (gpg) or mg/L. Hard water accelerates sca…
- Water Heater Element The electric resistance heating coil inside an electric water heater that heats the water. Most electric tanks have two element…
- Water Heater Flush The process of draining sediment from the bottom of a tank water heater to restore efficiency, extend tank life, and prevent ru…
- Water Meter The device installed by the water utility that measures water consumption in cubic feet or gallons. Reading it can detect hidde…
- Water Pressure The force at which water moves through your home's supply pipes, measured in PSI. Ideal residential pressure is 40–80 PSI — too…
- Water Softener A whole-house treatment system that removes calcium and magnesium ions (hardness minerals) from water through ion exchange, pre…
- Water Testing Laboratory or at-home analysis of drinking water to identify contaminants, assess water quality, and determine what treatment s…
- Wax Ring Soft wax gasket that seals the toilet base to the floor flange, blocking sewage and sewer gas from leaking around the bowl.
- Well Pump The pump that draws water from a private well and delivers it to the home's plumbing system. Submersible pumps (inside the well…
- Wet Vent A pipe that serves as both a drain for one fixture and a vent for another — allowed by plumbing codes in specific configuration…
- Wye Fitting A Y-shaped drain fitting that joins two drain lines at a 45-degree angle, allowing horizontal branch connections without the tu…
Need help right now?
Glossary entries answer "what is this?" — if you have an actual leak, burst pipe, or backed-up sewer, skip the reading and reach a verified plumber.