Homeowners A to Z of Residential Plumbing Terms

Understanding plumbing terms can make homeownership a lot easier. From simple fixtures like faucets and traps to essential safety devices like shutoff valves and backflow preventers, knowing the right words helps you talk confidently with plumbers, follow maintenance tips, and make smart upgrade decisions.

This U.S. glossary gathers the most common residential plumbing terms, codes, and associations into one resource, written in plain language for homeowners.

☑️ A

• ABS (acrylonitrile-butadiene-styrene): Black plastic pipe used in drain, waste, and vent systems.
• Access panel: Removable cover that lets you reach shutoffs or hidden plumbing.
• Adaptor (adapter): Fitting that connects different types or sizes of pipes.
• Aerator: Faucet tip screen that mixes air with water to reduce splashing.
• Air admittance valve (AAV): One-way vent that admits air to prevent trap siphonage (allowed in some states).
• Air chamber: Short pipe that cushions water hammer.
• Air gap: Vertical space between a faucet and sink to prevent backflow.
• Angle stop: Small shutoff valve under sinks or toilets.
• ANSI: U.S. standards body for plumbing and mechanical products.
• Anti-siphon valve: Prevents reverse flow caused by siphoning.
• Appliance (plumbing): Water-using device like a dishwasher or washing machine.
• Arrester (water hammer arrester): Device that absorbs shock when water flow stops suddenly.
• ASTM: Organization that sets specifications for pipe and fittings.
• Auger (plumber’s snake): Flexible cable used to clear clogs.

☑️ B

• Backflow: Reverse flow of water that can contaminate the supply.
• Backflow preventer: Device that keeps contaminated water from flowing into potable supply.
• Backwater valve: Valve that prevents sewage from backing into a home.
• Ball valve: Quarter-turn shutoff valve with a drilled ball inside.
• Ballcock (fill valve): Toilet tank valve that controls refill after flushing.
• Basin wrench: Tool for tightening nuts in hard-to-reach places under sinks.
• Bidet: Fixture or toilet attachment for personal cleansing.
• Black water: Wastewater from toilets containing human waste.
• Boiler: Appliance that heats water for heating systems.
• Booster pump: Pump that raises water pressure in low-pressure areas.
• Branch drain: Pipe that carries wastewater from fixtures to a larger drain.
• Brass: Copper-zinc alloy used in fittings and valves.
• BTU (British Thermal Unit): Unit of heat energy; used to rate heaters.
• Bushing: Fitting that reduces pipe size.
• Building drain: Horizontal pipe inside the building that carries waste to the sewer.
• Building sewer: Pipe that carries wastewater from the house to municipal sewer or septic system.
• Butterfly valve: Valve with a rotating disk to control flow.
• Bypass: Alternate piping route, such as around a water softener.

☑️ C

• Cast iron pipe: Heavy drain pipe used in older homes.
• Check valve: Valve that allows water to flow one way only.
• Cleanout: Access fitting for clearing blockages in drains.
• Closet auger: Auger tool designed to unclog toilets.
• Closet bend: Curved fitting connecting a toilet to the drain.
• Closet flange (toilet flange): Fitting that secures a toilet to the floor and drain pipe.
• Combination wye and 1/8 bend (combo): Fitting combining a wye and 45° elbow for smooth flow.
• Compression fitting: Fitting that seals with a nut and ferrule.
• Condensate drain: Pipe that carries condensation away from AC units or furnaces.
• Coupling: Short fitting that joins two pipes.
• Cross-connection: Connection between potable water and non-potable sources.
• Curb stop: Shutoff valve at the property line, usually owned by the water utility.
• CPVC (chlorinated polyvinyl chloride): Plastic pipe for hot and cold water.

☑️ D

• Diaphragm: Flexible membrane inside certain valves.
• Dip tube: Tube in a water heater that directs cold water to the bottom.
• Drain: Pipe that carries wastewater away from a fixture.
• Drain tile (French drain): Perforated pipe around a foundation that redirects groundwater.
• Drainage fixture unit (DFU): Unit used to size drain pipes.
• Drain cleaning: Process of removing clogs from drain lines.
• Drip leg (sediment trap): Pipe extension on gas lines that catches moisture or debris.
• Drop ear elbow: Elbow with mounting ears for securing to framing.
• Dual flush toilet: Toilet with two flush options to save water.
• DWV (drain, waste, vent): Piping system that removes wastewater and vents sewer gases.

☑️ E

• Ejector pump: Pump that moves sewage from a lower to a higher drain line.
• Elbow (ell): Fitting that changes pipe direction.
• Energy factor (EF): Rating of water heater efficiency.
• Escutcheon: Decorative plate covering a pipe hole.
• Expansion joint: Flexible connector allowing for thermal expansion.
• Expansion tank: Tank that absorbs pressure from expanding hot water.

☑️ F

• Faucet: Fixture that controls water flow.
• Ferrule: Ring inside a compression fitting that seals a connection.
• Fixture: Any water-using or draining device (toilet, sink, shower).
• Fixture unit: Value used to size plumbing systems.
• Flapper: Rubber valve in a toilet tank that lifts to flush.
• Flexible connector: Flexible pipe that connects fixtures or appliances.
• Float valve: Valve that shuts off toilet tank water when full.
• Floor drain: Drain set in floors to remove standing water.
• Flow restrictor: Insert that limits water flow in fixtures.
• Flushometer: Valve that delivers a measured flush (common in commercial restrooms).
• Flux: Paste used in soldering copper pipes.
• Frost-proof hose bibb: Outdoor faucet designed to prevent freezing in cold climates.

☑️ G

• Galvanized pipe: Zinc-coated steel pipe, common in older homes.
• Garbage disposal: Under-sink appliance that grinds food waste.
• Gasket: Flexible seal between two surfaces.
• Gas cock: Shutoff valve for a gas appliance.
• Gate valve: Valve that raises/lowers a gate to stop flow.
• Globe valve: Valve that throttles water flow.
• Gravity flush toilet: Standard toilet that uses gravity to flush.
• Gray water: Wastewater from sinks, showers, and laundry.

☑️ H

• Hard water: Water with high mineral content.
• Hose bibb (sillcock): Outdoor faucet for hose connection.
• Hot water heater (water heater): Appliance that heats water for home use.
• Hubless coupling: Rubber and clamp fitting used to connect pipes.
• Hydro jetting: High-pressure water method for clearing clogs.
• Hydronic heating: Heating system that uses circulating hot water.

☑️ I

• ID (inside diameter): Interior measurement of a pipe.
• Immersion heater: Electric element that directly heats water.
• Indirect water heater: Tank heated by a boiler.
• Interceptor: Device that traps grease, sand, or oil.
• Insulation (pipe insulation): Material that protects pipes from freezing and heat loss.
• Instantaneous water heater (tankless): Heats water on demand without storage.
• Isolation valve: Shutoff valve for a fixture or section of piping.

☑️ J

• J-bend: Curved part of a trap that holds water.
• J-hook: Pipe hanger shaped like a J.
• Jet pump: Pump that lifts water in shallow wells.

☑️ K

• Kitchen sink strainer: Basket fitting covering a sink drain opening.
• Kitec piping: Plastic-aluminum pipe used in 1990s–2000s, prone to failure.

☑️ L

• Lavatory: Bathroom sink.
• Lead: Soft metal once used in pipes, now banned.
• Leak detection: Process of finding hidden leaks.
• Liquid waste: Wastewater without solids.
• Loop vent: Vent pipe loop connected to the main vent.
• Laundry box: Recessed wall box for washer shutoffs and drain.
• Laundry tub (utility sink): Deep sink for laundry and cleaning.

☑️ M

• Main: Primary water or drain pipe in a system.
• Manifold: Hub that distributes water to branches.
• Mixing valve: Valve that blends hot and cold water.
• Moen cartridge: Cartridge controlling flow/temperature in Moen faucets.
• Mold: Fungus that grows in damp plumbing areas.
• Municipal water supply: Treated water provided by a utility.

☑️ N

• Neutralizer: Device that reduces acidity in drains.
• New plumbing installation: Installation of new plumbing lines and fixtures.
• Nipple: Short threaded pipe.
• No-hub coupling: Flexible coupling with clamps for cast iron pipes.

☑️ O

• Offset: Change in pipe direction.
• O-ring: Round rubber seal.
• OD (outside diameter): Exterior measurement of pipe width.
• Overflow tube: Tube in a toilet tank preventing overfilling.

☑️ P

• P-trap: Curved pipe under sinks that blocks sewer gases.
• PEX (cross-linked polyethylene): Flexible plastic piping for supply.
• Pipe dope (thread sealant): Paste for sealing threaded joints.
• Pipe hanger: Support for holding pipes in place.
• Pitch (slope): Angle that ensures drains flow properly.
• Plumber’s putty: Sealing compound for fixtures.
• Plumber’s tape (PTFE tape): Tape for sealing threaded connections.
• Plumbing snake: Flexible tool for unclogging drains.
• Polybutylene (Poly-B): Plastic pipe used in older homes, prone to leaks.
• Potable water: Safe drinking water.
• Pressure-balancing valve: Shower valve that maintains temperature balance.
• Pressure-reducing valve (PRV): Device that lowers incoming water pressure.
• Pump: Device that moves water in wells, sumps, or systems.
• P-trap primer: Device that adds water to traps to keep seals from drying out.

☑️ Q

• Quarter-turn valve: Valve that opens or closes with a 90° turn.
• Quick-connect fitting: Push-to-connect fitting for easy installation.

☑️ R

• Recirculation pump: Pump that circulates hot water for instant access.
• Reducer: Fitting that connects different pipe sizes.
• Relief valve: Safety valve that releases excess pressure or heat.
• Re-piping: Replacing old plumbing with new pipes.
• Retaining nut: Nut that secures faucet stems or valves.
• Riser: Vertical pipe that carries water upward.
• Rooter service: Professional drain clearing, often tree root removal.
• Rough-in: Initial installation of pipes before finishes.
• Roof vent (vent stack): Vertical pipe extending through the roof to vent sewer gases.
• Sewer lateral: Pipe that connects a home’s plumbing to the municipal sewer line.

☑️ S

• Sanitary tee: T-shaped fitting directing waste into a drain.
• Septic tank: Underground tank treating sewage for homes not on municipal sewer.
• Septic field (leach field): Underground system dispersing treated effluent into soil.
• Service call: Standard plumber visit fee.
• Service line: Pipe carrying water from the main to a house.
• Shutoff valve: Valve that stops water flow to fixtures.
• Slope (fall): Angle that ensures wastewater flows properly.
• Soil stack: Vertical pipe carrying waste from toilets.
• Stop-and-waste valve: Outdoor shutoff valve with a drain port.
• Sump pump: Pump that removes collected groundwater.
• Sweat fitting: Copper fitting joined with solder.
• Sediment trap: Pipe section that collects debris in gas lines.

☑️ T

• Tailpiece: Pipe between a fixture and its trap.
• Tankless water heater: On-demand water heating appliance.
• Tap: Another term for faucet.
• Temperature and pressure relief valve (T&P valve): Safety device on water heaters.
• Thermostatic mixing valve (TMV): Valve that maintains outlet water at a safe temperature.
• Trap: Curved pipe that holds water to block gases.
• Trap arm: Pipe section between a trap and vent.
• Trap primer: Device that adds water to traps automatically.
• Trap seal: Water in a trap that blocks sewer gases.

☑️ U

• Union: Fitting that connects two pipes but can be disconnected.
• Urinal: Wall-mounted fixture for liquid waste.
• Utility sink (laundry tub): Deep sink for laundry or cleaning.

☑️ V

• Valve: Device that controls water flow.
• Vent boot: Flashing around a roof vent pipe.
• Vent cap: Cover that keeps debris out of a vent stack.
• Vent pipe: Pipe that lets air into a drain system.
• Vent stack: Main vertical vent that exits through the roof.
• Vertical lift pump: Pump that moves water from low to high levels.

☑️ W

• Waste arm: Horizontal pipe from a trap to a drain.
• Washer: Flat ring that seals faucets or valves.
• Water hammer: Loud banging from sudden stoppage of flow.
• Water main: Large utility pipe supplying water to homes.
• Water meter: Device measuring water use.
• Water softener: Appliance that removes hardness minerals.
• Wax ring: Seal between a toilet base and flange.

☑️ Y

• Y-branch (wye): Fitting that joins a branch at a 45° angle.
• Yoke vent: Vent that connects a soil stack to a vent stack.

☑️ Z

• Zone valve: Valve that controls flow in heating system zones.
• Zoning (plumbing/heating): Dividing a system into independently controlled sections.

☑️ Standards & Codes (U.S.)

• International Plumbing Code (IPC): Model plumbing code adopted in many states.
• Uniform Plumbing Code (UPC): Code developed by IAPMO, adopted in several states.
• International Residential Code (IRC): Covers plumbing requirements for one- and two-family homes.
• National Standard Plumbing Code (NSPC): Code published by PHCC, still used in some areas.
• State Plumbing Codes: Each state adopts either IPC, UPC, or its own modifications.
• Local Amendments: City or county-level rules on top of state codes.

☑️ Associations & Trade Bodies (U.S.)

• Plumbing-Heating-Cooling Contractors Association (PHCC): National contractor group.
• American Society of Plumbing Engineers (ASPE): Professional organization for plumbing designers and engineers.
• International Association of Plumbing & Mechanical Officials (IAPMO): Developer of the Uniform Plumbing Code and product certifications.
• American Society of Sanitary Engineering International (ASSE International): Publishes standards for plumbing products.
• International Code Council (ICC): Publishes the International Plumbing Code and International Residential Code.
• American Water Works Association (AWWA): Organization focused on water supply and water quality.
• National Association of Home Builders (NAHB): Builder association with plumbing-related interests.
• United Association of Journeymen and Apprentices (UA): Union representing plumbers, pipefitters, welders, and HVAC technicians.
• Local Plumbing Boards: City or county agencies that license plumbers and enforce local plumbing codes.

Conclusion & Next Steps

Plumbing may seem complicated, but with the right vocabulary, it’s much easier to understand how your home’s systems work and when to call for help. This glossary gives you the basics, but there’s always more to learn about keeping your home safe, efficient, and comfortable.

👉 Keep exploring — check out more plumbing articles at DIY Home Comfort to dive deeper into tips, fixes, and guides every homeowner can use.

Scott Harding

Scott is the main author of DIY Home Comfort. He's also an experienced HVAC technician that enjoys home renovation and spending time with his family. You can find out more about him here.