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Plumbing Terminology
Extensive Online Plumbing Dictionary

Click on any letter of the term you would like to find

the barrier built into a trapway of a toilet that controls the water level in the toilet bowl.

Direct Current. Electrical supply in which the polarity of the two wires does not change.

Deck-Mount Faucet:
Term used to describe a faucet that is mounted on the deck of the bathtub enclosure, rather that on the rim of the bathtub or on the wall. Also known as a Roman spout faucet, or Roman tub faucet.

Deep Well:
A well more than 25 ft deep.

Degree Rise:
Difference between the starting water temperature and the ending temperature after heating is complete.

Process of reducing water to a non-mineral state by passing it over a bed of resins.

Deionized Water:
Water free of inorganic materials.

Desanco Fitting:
A type of compression adapter that connects tubular brass fittings to PVC pipe.

Dew Point:
Temperature at which water vapor condenses to a liquid.


Dial Plate:
Trim piece found behind a single-control wall-mount faucet handle. Also known as a face plate.

Flexible membrane in a valve that deflects down onto a rigid area of the valve body to regulate water flow from the supply lines. This eliminates the possibility of debris build-up within the valve.

Cutting device used to thread pipe. A set of these attach to dieheads, and mounted on a threader.

A nonconductor of direct electric current.

Dielectric Coupling:
Also known as an insulated coupling. Normally a galvanized steel coupling internally coated with ABS plastic to stop direct electrical current from passing through the pipe. Also used to connect dissimilar metal piping together to stop electrolysis or a chemical reaction. Example: connecting copper and galvanized.

Device for reducing the velocity and increasing the static pressure of a fluid passing through a system.

Dilution Air:
Air that enters a draft hood or draft regulator and mixes with the flue gasses.

Dip Tube:
Tube inside the water heater that sends cold water to the bottom of the tank.

Direct Tap:
Clamping device that allows a branch line to be drilled and tapped off a main line.

Direct Vent:
A system that pulls outside air for combustion and vents combustion gases directly outside without using a chimney.

Directional jet:
Whirlpool air discharge unit with pivot allowing discharge path to be adjusted by the user.

Directional Tee:
Tee fitting that allows direct flow in one direction by use of an internal baffle.

Discharge Head:
Difference in elevation between the liquid level of the discharge tank and the centerline of the pump. Also includes any additional pressure head that may be present at the discharge tank fluid surface.

Discharge Tube:
Outlet tube that connects a disposer or sump pump to the drain line.

Dishwasher Tailpiece:
A flanged adapter connecting a basket strainer to the drainpipe with a dishwasher inlet.

Disposal Field:
A series of trenches conveying the effluent from the septic tank laid in such a manner that flow will be distributed with reasonable uniformity into natural soil.

Valves which direct water to various outlets. They are used in showers, tub & shower combinations, bidets, roman tub fillers, and kitchen faucet sprayers.

Diverter Valve:
valve which redirects flow of water to another application within a plumbing system. It is commonly used for diverting water from the tub faucet to a showerhead.

Domestic Hot Water:
Water heated for residential washing, bathing, etc.

pasty lubricant used on a seal pipe threads prior to making a threaded pipe connection.

Double Extra Strong:
Standard pipe weight designation. Sometimes described as XXH.

Double Horizontal Tee:
A PVC tee with twin outlets of a smaller diameter than the inlet.

Double Sink (Double Basin):
Sink which offers two separate basins.

Double Suction Pump:
A pump where the rotor is suspended between two bearings with the fluid entering on either side of the impeller. Used at higher capacities.

Double Threshold:
A shower base used in a corner application where one threshold is used as an entrance and the other has a glass wall.

Double Wye Fixture:
A fitting that has branches coming in at an angle from each side of the main to join the main run.

Down Head Boring Gimlet:
A flexible cutting tip for an auger cable.

Draft Diverter:
A device fitted in the flue way of a gas appliance to prevent updraft, downdraft, or the secondary flue blockage from obstructing the escape of combustion gases.

Any pipe which carries off water or water-born wastes in a plumbing drainage system.

Drain Body:
The portion of a drain fitting which receives the stopper.

Drain Hub:
Floor drain used with hubbed soil pipe. The bell section is countersunk vertically in the floor and is covered by a flush-mounted grill.

Drain Lever:
A lever assembly secured to a drain body to lift a stopper and allow water to leave a basin. Also known as ball lever.

Drain Linkage:
An adjustable strap or bar forming a connection between the lift rod of a faucet and the ball lever assembly of the drain. Also known as connection link.

Drain Seal Gasket:
gasket used to seal a drain to a sink to prevent leaks.

Drain Valve:
Device designed to allow drainage of stored contents from a water heater.

Drainage Tile:
Historically, pipe shaped clay tiles installed in below-grade trenches for gravity-rated drainage. PVC pipe is now commonly used for this purpose.

The distance the water level drops below the standing water level while the pump is operating.

Drip Channel:
A metal channel that is designed to prevent water running down a shower door from dripping onto the floor when the door is opened.

Drip Irrigation:
A common irrigation method where pipes or tubes filled with water slowly drip onto crops. Drip irrigation is a low-pressure method of irrigation and less water is lost to evaporation than high-pressure spray irrigation.

Drip Leg:
A stub end pipe placed at a low point in the gas piping to collect condensate and permit its removal.

Drop-In Sink:
Style of bathtub or whirlpool bath which includes an integral mounting rim as part of the overall structure.

Drum Trap:
An obsolete, non-vented drain lead or cast iron canister trap formerly used in sewer lines.

Dual Element Heater:
An electric water heater with an upper and lower element for heating water.

Sink drain fitting consisting of a strainer body attached to the drain opening and a removable basket. Also called a strainer.

A twin valve (hot & cold) with a single on/off lever used for washing machine boxes.

Duplex Basin:
An ejector pump container, large enough for two pumps, used in multi-family buildings.

A process patented by Ace Duraflow company to rejuvenate old corroded plumbing by cleaning and lining with an epoxy coating.

Drainage, Waste, and Vent systems, which remove wastewater. Not for drinking water.

Dynamic Pressure:
The pressure when the water is flowing.