Plumbing Glossary

ABS Drain Pipe

ABS drain pipe is black plastic pipe made from acrylonitrile-butadiene-styrene, sized to Schedule 40 iron pipe dimensions and used for a building’s drain, waste and vent lines, not for pressurized drinking water.

Activated Carbon Water Filter

An activated carbon water filter is a filter that passes water through highly porous carbon, made from coal, wood or coconut shell and heat-treated to open millions of tiny pores, so chlorine, bad tastes and odors, and many organic chemicals stick to the carbon surface and stay behind.

Air Admittance Valve (AAV)

An air admittance valve (AAV) is a one-way mechanical vent that opens to let room air into a drain pipe when draining water creates suction, then closes to keep sewer gas in, so the fixture’s trap is not siphoned dry.

Atmospheric Vacuum Breaker

An atmospheric vacuum breaker (AVB) is a simple backflow device with a float, a seal and an air port that lets air into a water line when supply pressure drops, so water from a hose, sprinkler zone or fixture cannot be siphoned back into the drinking water pipes.

Backflow Prevention Device

A backflow prevention device is a fitting, valve assembly or air gap placed in a water line so that water can flow only one way, keeping used, chemical or dirty water from being pushed or siphoned back into the drinking water supply.

Bidet Toilet Seat

A bidet toilet seat is a replacement toilet seat with a built-in wand that sprays water for personal washing, fed by a tee on the toilet’s cold water supply line and, on electric models, plugged into a nearby outlet to heat the water and seat.

Burst Pipe

A burst pipe is a water supply pipe that has split, cracked open or blown apart at a joint, letting water escape under full house pressure, most often after the water inside froze and the trapped pressure behind the ice became more than the pipe could hold.

Cast Iron Drain Pipe

Cast iron drain pipe is heavy pipe cast from gray iron and used for a building’s drain, waste, vent and sewer lines, joined either with rubber-gasketed hubs or with hubless couplings, and valued for strength, low noise and fire resistance.

Copper Plumbing Pipe

Copper plumbing pipe is round tube made of at least 99.9 percent copper, sold in hard and soft tempers and in wall thicknesses called Types K, L and M, that carries drinking water through homes and is joined with solder, brazing, flare, press or push fittings.

CPVC Plumbing Pipe

CPVC plumbing pipe is rigid chlorinated polyvinyl chloride pipe made for hot and cold drinking water lines, joined with solvent cement and sized to match copper tube, with one maker rating its pipe at 100 psi continuous at 180°F.

Cross-Connection in Plumbing

A cross-connection in plumbing is any actual or potential connection between a drinking water line and a source of pollution or contamination, such as a hose in a chemical bucket, a boiler fill line or a lawn sprinkler system.

Dielectric Union

A dielectric union is a pipe union that joins two different metals, usually copper and steel, with a plastic insulator and gasket between the halves, so electric current cannot flow from one metal to the other and speed up galvanic corrosion at the joint.

Drain Auger

A drain auger is a plumbing tool made of a flexible coiled-steel cable that is pushed and rotated into a drain line to break up, hook or pull out a clog, worked by hand crank or by an electric motor.

Drain-Waste-Vent (DWV) System

A drain-waste-vent (DWV) system is the network of sloped pipes, traps and vents in a building that carries used water and sewage by gravity to the sewer or septic system while letting air in and out so drains flow smoothly and sewer gas stays out.

Drainage Fixture Unit (DFU)

A drainage fixture unit (DFU) is a code-assigned number that rates how much load one plumbing fixture puts on a drain, so the units from every fixture on a pipe can be added up and checked against the largest load that pipe size is allowed to carry.

Drinking Water pH

Drinking water pH is a measure of how acidic or basic tap water is, on a scale from 0 to 14 where 7 is neutral; the U.S.

Ejector Basin: see Sewage Ejector Pump

Electronic Water Leak Detection

Electronic water leak detection is the use of battery or plug-in devices that sense water where it should not be, or track how much water flows through the pipes, and then sound an alarm, send a phone alert or close a valve when they spot a likely leak.

Faucet Aerator

A faucet aerator is the small screw-in or screw-on insert at the tip of a faucet spout that mixes air into the water or straightens it, filters out grit with a screen, and limits how many gallons per minute the faucet can deliver.

Faucet Cartridge

A faucet cartridge is the removable valve inside a faucet or shower handle that opens, closes and mixes the hot and cold water as you move the handle, using sliding seals or ceramic discs inside a plastic or brass body.

Floor Drain

A floor drain is a grated drain set into a floor, usually in a basement, laundry room, garage or utility room, that collects water from spills, leaks or overflows and carries it through a trap into the building’s drain system.

Frost-Proof Hose Bibb

A frost-proof hose bibb is an outdoor wall faucet with a long stem that puts its shutoff valve several inches inside the heated house, so the part outside drains empty when you turn it off and has no water left to freeze.

Galvanized Steel Plumbing Pipe

Galvanized steel plumbing pipe is iron or steel pipe dipped in zinc to slow rust, joined with threaded fittings, and found mostly in older homes as water supply lines and sometimes drain lines.

Grinder Pump

A grinder pump is an electric sewage pump, set in an underground tank on a property, that chops household wastewater into a fine slurry and pushes it under pressure through a small pipe to the public sewer when the sewage cannot flow there by gravity.

Heat Pump Water Heater

A heat pump water heater is an electric storage water heater that uses a small refrigeration cycle to pull heat from the surrounding air and move it into a tank of water, with electric elements as backup.

Hot Water Recirculation Pump

A hot water recirculation pump is a small pump that moves water from the hot water pipes back to the water heater, so hot water is already near the tap when you open it instead of after the cooled water in the pipe has run down the drain.

Hydro Jetting

Hydro jetting is a drain and sewer cleaning method that sends water at high pressure through a hose and nozzle into a pipe, where the jets scour grease, sludge, debris and roots off the pipe walls and flush them downstream.

Indirect Waste Connection

An indirect waste connection is a drain from a fixture or piece of equipment that does not tie straight into the sanitary drain, but empties through an open air gap or air break into a separate receptor, such as a floor sink or standpipe, so sewage can never back up into the equipment.

Ion-Exchange Water Softener

An ion-exchange water softener is a tank of resin beads that removes hardness from water by trading the calcium and magnesium in it for sodium (or potassium) ions, then rinses itself with salt brine to recharge.

Licensed Master Plumber

A licensed master plumber is a plumber who has passed a state or local master-level exam after years of licensed journeyman work, and who may plan plumbing work, supervise journeymen and apprentices, and, in many states, run a plumbing business or pull permits.

Main Sewer Line

A main sewer line, for a house, is the single underground pipe that carries all of the home’s wastewater from the building drain out to the public sewer main in the street or an easement, and in many places the property owner is responsible for it along its whole length.

Main Water Shutoff Valve

A main water shutoff valve is the valve on the pipe that brings water into a house, placed near where that pipe enters, that stops the flow to every fixture at once so a leak or repair can be handled without calling the water utility.

PEX Plumbing Pipe

PEX plumbing pipe is flexible water supply tubing made from cross-linked polyethylene, a plastic whose molecules are chemically bonded to each other so it holds up to hot, pressurized, chlorinated drinking water.

Pinhole Leak in Copper Pipe

A pinhole leak in copper pipe is a very small hole that forms when corrosion eats through the pipe wall from the inside at one spot, a process called pitting, letting water spray or seep out while the rest of the pipe still looks sound.

Plumbing Check Valve

A plumbing check valve is a one-way valve that lets water or wastewater flow in only one direction and closes automatically, using a hinged flap, spring-loaded disc or ball, when flow stops or tries to reverse, so the pipe cannot drain backward.

Plumbing Dye Test

A plumbing dye test is a check in which colored water is added to a toilet tank, drain, downspout or septic system and watched for somewhere else, to prove where water flows: from a tank into the bowl, a roof drain into the sewer, or a septic system to the surface.

Plumbing Expansion Loop

A plumbing expansion loop is a U-shaped bend, coil or offset built into a long straight pipe run, usually a hot water line, so that the pipe can lengthen and shorten as its temperature changes without pushing on fittings, buckling or cracking joints.

Plumbing Expansion Tank

A plumbing expansion tank is a small pressurized tank on the cold water line of a water heater that takes in the extra water created as the heater warms it, so pressure in a closed house water system stays below the relief valve setting.

Plumbing Flow Rate

Plumbing flow rate is the volume of water that moves through a pipe or out of a fixture in a set time, usually stated in gallons per minute (gpm), and it is what decides how fast a tub fills or how strong a shower feels.

Plumbing Inspection Report

A plumbing inspection report is a written record of what an inspector checked in a building’s plumbing, such as supply and drain pipes, fixtures, the water heater and shutoff valves, what they found, and which items are deficient or need a licensed plumber.

Plumbing Leak Isolation

Plumbing leak isolation is the process of closing valves one zone at a time, such as the main shutoff, the irrigation line or a single fixture, and watching the water meter to learn which part of the system is losing water before anyone opens a wall.

Plumbing P-Trap

A plumbing P-trap is the curved section of drain pipe under a sink, tub or shower that stays filled with water, forming a seal that lets waste drain out while blocking sewer gas from coming back into the room.

Plumbing Permit

A plumbing permit is written approval from a city or county building department to install, alter, repair or replace plumbing, issued before the work starts and closed out only after an inspector checks the work against the adopted plumbing code.

Plumbing Pipe Insulation

Plumbing pipe insulation is a sleeve or wrap of foam, fiberglass or similar material fitted around water pipes to slow heat flow, so hot water lines lose less heat on the way to a fixture and cold lines in unheated spaces are less likely to freeze.

Plumbing Pipe Schedule

A plumbing pipe schedule is a standard number, such as Schedule 40 or Schedule 80, that sets how thick a pipe’s wall is for a given nominal size, while the outside diameter stays the same, so a higher schedule means a thicker wall, a smaller inside bore and a higher pressure rating.

Plumbing Pressure Gauge: see Residential Water Pressure

Plumbing Pressure Test

A plumbing pressure test is a leak check in which new, repaired or suspect piping is sealed and filled with water or air at a set pressure, or a set height of water, and watched for a fixed time to prove it holds without dropping or leaking.

Plumbing Preventive Maintenance

Plumbing preventive maintenance is the routine inspection, testing and servicing of a home’s pipes, fixtures, water heater, pumps and valves on a schedule, done to catch wear before it becomes a leak, a freeze, a backup or a failed appliance.

Plumbing Rough-In

Plumbing rough-in is the stage of a build or remodel when the hidden pipes are installed and tested: drains, vents, water supply lines and fixture stub-outs are run through the framing or under the slab, before walls, floors and fixtures go in.

Plumbing Service Agreement

A plumbing service agreement is a paid contract between a homeowner and a plumbing company that sets out scheduled maintenance visits, inspections and repair terms for a fixed period, often with priority scheduling or reduced service fees.

Plumbing Smoke Test

A plumbing smoke test is an inspection in which non-toxic smoke is blown into a drain, vent or sewer system under light pressure, so that it escapes and becomes visible wherever pipes are cracked, joints are open, traps are dry or storm drains are wrongly connected.

Plumbing Trap Primer

A plumbing trap primer is a valve or device that adds a small amount of water to a drain trap, usually a floor drain, so the water seal does not evaporate and let sewer gas into the building.

Plumbing Vent Stack: see Plumbing Venting

Plumbing Venting

Plumbing venting is the network of air pipes connected to a home’s drains that lets air in and out as water flows, so the pressure in the drains stays balanced and the water seal in each fixture trap is not sucked out or pushed through.

Plumbing Water Hammer Arrestor: see Water Hammer

Potable Water System

A potable water system is the pressurized network of pipes, valves and fixtures that carries water safe to drink from a public main or private well to every tap in a building, kept separate from drains and any non-drinking water.

Pressure-Balancing Shower Valve

A pressure-balancing shower valve is a single-handle shower control that senses the hot and cold supply pressures and automatically throttles one side when the other drops, so the mixed water temperature stays steady when someone flushes a toilet or runs a tap.

Pressure-Reducing Valve (PRV)

A pressure-reducing valve (PRV) is a spring-and-diaphragm valve on a home’s incoming water line that automatically lowers high, changing street pressure to a steady, adjustable set point, so pipes, fixtures and appliances inside the house are not exposed to excess pressure.

PVC Plumbing Pipe

PVC plumbing pipe is rigid pipe made of polyvinyl chloride, a plastic, joined with primer and solvent cement and used in homes mainly for drain, waste and vent lines and for cold water service lines, because it does not rust and is light to work with.

Residential Drain Line

A residential drain line is any pipe in a house that carries used water and waste away from sinks, tubs, toilets and appliances, flowing by gravity on a steady downward slope to the building drain and then to the sewer or septic system.

Residential Plumbing System

A residential plumbing system is the set of pipes, valves, fixtures and appliances in a home that brings in clean water under pressure, heats and delivers it to taps, and carries used water and waste out by gravity to a public sewer or septic system.

Residential Water Pressure

Residential water pressure is the force that pushes water through a home’s supply pipes, measured in pounds per square inch (psi), usually read as static pressure with no water running.

Residential Well Pump

A residential well pump is the electric pump that lifts groundwater from a private well and pushes it into the home’s pressure tank and pipes, either from inside the well below the water level (a submersible pump) or from the surface by suction (a jet pump).

Reverse Osmosis Water Filtration

Reverse osmosis water filtration is a treatment method that uses water pressure to force water through a semi-permeable membrane, so treated water passes through and many dissolved contaminants are rejected and flushed down the drain.

Sediment Water Filter

A sediment water filter is a mechanical filter, usually a replaceable cartridge in a plastic housing, that strains suspended particles such as sand, silt, loose scale, clay and rust out of water as it flows through.

Septic Tank Effluent Filter

A septic tank effluent filter is a removable screen, usually a slotted cylinder set inside the tank’s outlet tee, that catches solids still floating in the treated wastewater before that liquid flows out to the drainfield.

Sewage Ejector Pump

A sewage ejector pump is a submersible pump set in a sealed, vented basin below floor level that collects waste from basement toilets, showers and sinks and pumps it up and out to the gravity sewer or septic line when a float switch senses the basin filling.

Sewer Camera Inspection

A sewer camera inspection is a check of a sewer or drain line in which a technician pushes a small waterproof video camera on a cable through the pipe to record its inside condition, such as cracks, roots, sags, offset joints and blockages.

Sewer Cleanout

A sewer cleanout is a capped fitting on a drain or sewer pipe, usually a short vertical pipe near the house or in the yard, that lets a plumber open the line to clear clogs and run a camera without pulling a toilet or digging.

Sewer Lateral: see Main Sewer Line

Shower Mixing Valve

A shower mixing valve is the valve behind a shower handle that blends hot and cold supply water to the temperature you choose and, in modern codes, must be a pressure-balance or thermostatic type with a stop that limits the hottest setting to 120°F.

Slab Leak

A slab leak is a leak in a water supply or drain pipe that runs under or inside a home’s concrete slab foundation, where the escaping water is hidden by the concrete and often shows up first as a high water bill, a warm floor spot or the sound of running water.

Storage Tank Water Heater

A storage tank water heater is an appliance that heats water inside an insulated tank and holds it at a set temperature, so hot water is ready the moment a tap opens.

Sump Pump

A sump pump is an electric pump that sits in a pit, called a sump, in the lowest part of a basement or crawlspace and pumps out groundwater that drains into the pit before it can rise onto the floor.

Tankless Water Heater

A tankless water heater is a water heater that warms water only while a hot tap is open, using a gas burner or electric elements and a heat exchanger instead of a storage tank.

Temperature and Pressure Relief Valve

A temperature and pressure relief valve (T&P valve) is a spring-loaded safety valve on a water heater that opens automatically and discharges water if the tank gets too hot or the pressure inside climbs too high.

Thermal Expansion in Plumbing: see Plumbing Expansion Tank

Toilet Fill Valve

A toilet fill valve, also called a ballcock, is the valve inside a toilet tank that opens after a flush to let in fresh water, refills both the tank and the bowl, and closes when a float tells it the tank has reached the set level.

Toilet Flange

A toilet flange, called a closet flange in plumbing codes, is the round fitting fastened to the top of a toilet drain pipe and the floor that holds the closet bolts, supports the toilet and gives the wax ring or gasket a flat face to seal against.

Toilet Flapper

A toilet flapper is the hinged rubber or plastic seal at the bottom of a toilet tank that lifts when you flush to release water into the bowl, then drops back onto the flush valve opening to hold the next tankful.

Toilet Flush Valve

A toilet flush valve is the assembly in the floor of a toilet tank, made of a drain opening, a sealing seat and an overflow tube, that releases the stored water into the bowl when the flapper or seal lifts and catches overflow if the tank overfills.

Toilet Wax Ring

A toilet wax ring is a thick ring of soft wax pressed between the bottom of a toilet and the floor flange that seals the joint, so waste water goes down the drain and sewer gas stays out of the room.

Total Dissolved Solids (TDS)

Total dissolved solids (TDS) is the combined amount of minerals, salts, metals and small amounts of organic matter dissolved in water, usually reported in milligrams per liter (mg/L), which equals parts per million (ppm).

Trap Arm: see Plumbing P-Trap

Tree Root Intrusion in Sewer Pipes

Tree root intrusion in sewer pipes is when roots grow into a sewer line through a crack, leak or loose joint, then keep growing inside on the water and nutrients in the wastewater until they slow drainage, catch debris and can break the pipe.

Trenchless Sewer Pipe Lining

Trenchless sewer pipe lining is a way to repair a damaged sewer pipe from the inside by pulling or turning a resin-soaked fabric tube into the old pipe and hardening it in place, forming a new pipe within the old one without digging a full trench.

Water Hammer

Water hammer is a pressure surge in a water pipe that happens when flowing water is stopped or turned suddenly, usually by a fast-closing valve, sending a shock wave through the pipe that you hear as a bang or knock.

Water Hardness

Water hardness is the amount of dissolved calcium and magnesium in water, usually reported as milligrams per liter (mg/L) of calcium carbonate or as grains per gallon (gpg).

Water Heater Anode Rod

A water heater anode rod is a long metal rod, usually magnesium or aluminum, screwed into the top of a tank water heater that corrodes on purpose so the steel tank does not, which is why it is called a sacrificial anode.

Water Heater Dip Tube

A water heater dip tube is a long plastic tube attached to the cold water inlet of a storage tank water heater that carries incoming cold water down to the bottom of the tank, so it is heated there and does not mix with the hot water drawn from the top.

Water Heater First-Hour Rating

Water heater first-hour rating (FHR) is the federal test estimate of the most hot water, in gallons, that a storage water heater can deliver in one hour starting from a fully heated tank, and it depends on both the tank’s storage volume and its recovery rate.

Water Heater Recovery Rate: see Water Heater First-Hour Rating

Water Heater Sediment Buildup

Water heater sediment buildup is the layer of mineral scale, sand and grit that settles on the bottom of a storage water heater over time, mostly calcium and magnesium that drop out of hard water when it is heated, which insulates the burner or element from the water and crowds the tank.

Water Meter

A water meter is the device, usually in a box near the curb or in a basement, that measures the volume of water flowing from the utility’s pipe into a property, so the utility can bill for it and you can track use and spot leaks.

Water Supply Fixture Unit (WSFU)

A water supply fixture unit (WSFU) is a code-assigned number that rates how much demand one plumbing fixture or bathroom group puts on the water supply pipes, so the units can be added and converted into a probable peak flow in gallons per minute for sizing the water service, meter and branches.

Water-Powered Backup Sump Pump

A water-powered backup sump pump is an emergency pump that uses the pressure of a home’s municipal water supply, not electricity, to draw water out of a sump pit when the main electric pump fails or the power goes out.

Well Pressure Tank

A well pressure tank is a sealed steel tank, usually holding a rubber bladder or diaphragm with compressed air around it, that stores well water under pressure so taps get water while the pump is off and the pump starts and stops less often.

Well Pump Foot Valve

A well pump foot valve is a one-way check valve with a built-in strainer screen, fitted to the bottom end of a suction pipe in a well, that lets water flow up to an above-ground pump and stops it from draining back down when the pump shuts off.

Whole-House Repiping

Whole-house repiping is replacing all of a home's water supply pipes, usually old galvanized steel, polybutylene or failing copper, with new PEX or copper run to every fixture, then patching the walls that were opened.

Whole-House Water Filter

A whole-house water filter is a point-of-entry treatment unit installed on the main water line where it enters a home, so every faucet, shower and appliance receives filtered water.