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Plumbing Terminology

Torrance Plumbing Dictionary I-Z

Here we have a continuation of the first round of plumbing terms A-H, to finish out the glossary that helps anyone from novice to pro keep up to date on important definitions.

Glossary Terms I-Z

In-Line Pump

Also known as straight-line pumps, these are small pumps that use centrifugal force, so the suction and discharge connections are in line with each other for a smooth flow.

Insert Fittings

Typically used as a means of connection, these sleeve-like pipe fittings have rings or barbs for gripping and are made from either plastic, nylon, or PVC.

Instantaneous Water Heater

This is another term for tankless water heaters, or heaters that instantly warm water as it flows through the device without using a storage tank.

J Bend

This has several names and types (think P-Trap U-Bend, S-Trap, etc.), but refers to the curved pipe underneath a sink that traps sewer gases.


Johni-Bolts are used to mount toilet bowls to the closet flange with a wax ring to prevent leaks.


Also known as a downspout, this is a pipe that drains rainwater down the side of buildings from gutters.

Main Line

The branch pipes around your home receive water from the main line of a water company’s meter.

Maximum Contaminant Level (MCL)

This is the maximum level of any contaminant allowed in water by federal law.

Mixing Valve

A valve that allows hot and cold water to mix together to reach specific temperatures.


A short length of pipe that connects fittings with tightly threaded ends.

No Hub (Hubless) Pipe

A pipe that has no threading and requires a specific connector to seal hubless pipes together.


A round rubber gasket that sits into a groove and compresses during the joining of two or more pipe lengths to create a watertight seal.

Outside Diameter

The outside measurements of a pipe.


A small faucet used to relieve air pressure or drain liquids.


Plastic tubing that is flexible for water supply line usage.

Power Flush System

This system compresses water to create a pressurized flush, particularly for commercial use.

Pressure Reducing Valve (PRV)

A valve that is installed directly on the main water line to control the amount of water entering the line from the water company’s supply for normal home use.


Sturdy plastic pipes used for drainage, waste, and ventilation.

Rim Holes

These are a series of small holes around the toilet bowl to refill the bowl after flushing.

Saddle Valve

A saddle valve is a pipe that is mounted to a surface and run by a clamping device to create quick connections between devices with low demand.

Septic Tank

Often used in homes with no connection to local sewage systems, septic tanks are small sewage treatment systems that use bacteria to decompose waste.

Sewer Gas

Toxic and potentially combustible gas resulting from organic material decaying in a sewer system – typically comprising of:

  • Hydrogen sulfide
  • Ammonia
  • Methane
  • Carbon dioxide
  • Sulfur dioxide
  • Nitrous oxides

Slip Joint

A connection made using compression fittings.

Soft Water

Water with a low amount of dissolved salts of calcium, iron, or magnesium which are harsh on plumbing systems.

Sump Pump

Sump pumps are useful for lower spaces such as basements which are prone to flooding because they sit in a pit that collects the water and reroutes it away from the home.

Supply Line

A plastic or metal line that carries water from the main line into a plumbing system.

Temperature and Pressure (T&P) Valve

This valve is used to safely release excess pressure or heat in a water tank.


A pipe that runs between a fixture and a trap.


A curved section of the drain line that is designed to prevent sewer odor from entering a space.


The passage that connects the toilet bowl to a waste outlet.

Trip Lever

The trip level is the flush handle, which is attached to the flapper to result in the toilet flushing. It can also be referred to as the drain in a tub.


A pipe that allows air into a drain system.

Vent Stack

Also known as a stink pipe, the vent stack is an outlet pipe that releases gas and odors outside the facility.

Voral Tube

A flexible hose made from steel for hand-held showerheads.

Waste Arm

A pipe used to extend a sink drain into a wall.

Waste Hammer

A loud noise caused by a sudden surge or halt of water in the pipes – this is associated with pipes being turned on or off.

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