Plumbing Terms

AAV (Air Admittance Valve)

AAV is a one-way valve designed to allow air to enter the plumbing drainage system when negative pressures develop in the piping system. The device shall close by gravity and seal the vent terminal at zero differential pressure (no flow conditions) and under positive internal pressures. The purpose of an air admittance valve is to provide a method of allowing air to enter the plumbing drainage system without the use of a vent extended to open air and to prevent sewer gases from escaping into a building.

ABS Pipe/Fittings

Acrylonitrile Butadiene Styrene, A common thermoplastic polymer used in Non-pressure DWV systems.  

Air Break (Drainage System)

A piping arrangement in which a drain from a fixture, appliance or device discharges indirectly into another fixture, receptacle or interceptor at a point below the flood level rim and above the trap seal.

Air Gap (Drainage System)

The unobstructed vertical distance through the free atmosphere between the outlet of the waste pipe and the flood level rim of the receptacle into which the waste pipe is discharging.

Air Gap (Water Distribution System)

The unobstructed vertical distance through the free atmosphere between the lowest opening from any pipe or faucet supplying water to a tank, plumbing fixture or other device and the flood level rim of the receptacle.


American Society of Safety Engineers. ASSE’s product standards are minimum performance requirements for component parts of the plumbing system. 


ASTM International, formerly known as the American Society for Testing and Materials. ASTM standards are used around the world to improve product quality, enhance safety, facilitate market access and trade, and build consumer confidence.

Backwater Valve

A device or valve installed in the building drain or building sewer pipe where a sewer is subject to backflow, and which prevents drainage or waste from backing up into a lower level or fixtures and causing a flooding condition.  

Bathroom Group

A group of fixtures consisting of a water closet, lavatory, bathtub or shower, including or excluding a bidet, an emergency floor drain or both. Such fixtures are located together on the same floor level.

Building Drain

That part of the lowest piping of a drainage system that receives the discharge from soil, waste and other drainage pipes inside and that extends 30 inches (762 mm) in developed length of pipe beyond the exterior walls of the building and conveys the drainage to the building sewer.

  • Combined or Combination - A building drain that conveys both sewage and storm water or other drainage.

  • Sanitary – A building drain that conveys sewage only.

  • Storm – A building drain that conveys storm water or other drainage, but not sewage.

Building Sewer

That part of the drainage system that extends from the end of the building drain and conveys the discharge to a public sewer, private sewer, individual sewage disposal system or other point of disposal.

  • Combined or Combination – A building sewer that conveys both sewage and storm water or other drainage.

  • Sanitary – A building sewer that conveys sewage only. 

  • Storm – A building sewer that conveys storm water or other drainage, but not sewage.


CPVC Pipe/Fittings

Chlorinated polyvinyl chloride (CPVC) is a thermoplastic produced by chlorination of polyvinyl chloride (PVC) resin. Uses include hot and cold water pipes, and industrial liquid handling.


DFU (Drainage Fixture Unit)

Drainage (DFU). A measure of the probable discharge into the drainage system by various types of plumbing fixtures. The drainage fixture-unit value for a particular fixture depends on its volume rate of drainage discharge, on the time duration of a single drainage operation and on the average time between successive operations.


Drainage Waste and Vents


Flood Level Rim

The edge of the receptacle (fixture) from which water overflows.



The International Association of Plumbing and Mechanical Officials (IAPMO), coordinates the development and adaptation of plumbing, mechanical, swimming pool and solar energy codes to meet the specific needs of individual jurisdictions both in the United States and abroad. IAPMO develops and publishes the Uniform Plumbing Code (UPC); Uniform Mechanical Code (UMC); Uniform Swimming Pool, Spa and Hot Tub Code (USPSHTC); Uniform Solar Energy Code (USEC); and the Green Plumbing and Mechanical Code Supplement (GPMCS).


International Plumbing Code


Non-Potable Water

Water not safe for drinking, personal or culinary utilization.


National Plumbing Code of Canada


National Pipe Straight Mechanical thread. This means the male and female threads are straight without taper.


National Pipe Thread. This means that the male thread is tapered and the further you thread the pipe into the fitting, it becomes tighter and creates the seal. The same taper is mirrored inside the fitting with the smallest diameter at the base of the female thread. 


NSF International was formerly known as the National Sanitation Foundation. It is a not for profit organization that provides public health and safety risk management solutions. Among those solutions, NSF International provides standards development and product certification. Foodservice and restaurant supply products that are certified by NSF undergo and have passed an evaluation to ensure that the product and facility where the product is made meet NSF standards for food safety. NSF standards are generally accepted by government regulatory agencies.



PEX pipe is a cross-linked thermo set material made from medium or high density polyethylene that meets ASTM F 876 and F 877 requirements, CSA, IAPMO, SBCCI, BOCA, ICBO, IPC, NSPC and HUD. The “cross-linking” of molecules make PEX an excellent choice for hot/cold water applications. PEX can be used in applications that have extreme temperature fluctuations ranging from below zero up to 200°F; this also makes PEX great for sinks, icemakers, dishwashers and refrigerators. PEX is also resistant to most household chemicals. 

Potable Water

Water free from impurities present in amounts sufficient to cause disease or harmful physiological effects and conforming to the bacteriological and chemical quality requirements of the Public Health Service Drinking Water Standards or the regulations of the public health authority having jurisdiction.

Public Sewer

A sanitary sewer is an underground drain system specifically designed for transporting sewage from houses and commercial buildings through pipes for treatment or disposal. Sanitary sewers are distinguished from open sewers in that the sanitary system is closed off from its surroundings to limit interaction between the waste and the landscape that it travels through. They are also usually distinguished from combined sewers, which handle not only sewage but also surface runoff. 


Polyvinyl Chloride


Sewer Gases

Sewer gas is a complex mixture of toxic and nontoxic gases produced and collected in sewage systems by the decomposition of organic household or industrial wastes, typical components of sewage. Sewer gases may include hydrogen sulfide, ammonia, methane, carbon monoxide, sulfur dioxide, and nitrogen oxides.



Uniform Plumbing Code

UL Listing

Underwriters Laboratories (UL) is an organization primarily dedicated to product safety. UL develops safety standards dealing with design, electrical, materials, components, and manufacturing. Products that carry a UL certification mark have been found to comply with UL standards for product safety.



Volatile Organic Compounds (VOCs) are a large group of carbon-based chemicals that easily evaporate at room temperature. While most people can smell high levels of some VOCs, other VOCs have no odor. Odor does not indicate the level of risk from inhalation of this group of chemicals. 


Water Closet

Another term for toilet