Plumbing terms, explained for beginners

Plain-English definitions from official sources · Last reviewed October 12, 2026

A

ASSE International

Also called: ASSE

ASSE International writes standards for plumbing products and for the people who work on certain systems, and it certifies both. Its best-known worker standards cover cross-connection control (backflow testers, Series 5000) and medical gas work (Series 6000, including 6010 for installers). ASSE says its standards are developed under the American National Standards Institute's accredited process. [9][10]

B

Backflow

Backflow is water, or anything else in the pipes, flowing the wrong way. Wisconsin's plumbing code, for example, defines it as "the unwanted reverse flow of liquids, solids or gases." It can happen when pressure in the water supply drops (back siphonage) or when pressure on the dirty side gets higher (back pressure). EPA (U.S. Environmental Protection Agency) says backflow through a cross-connection "can result in a potentially serious public health hazard." That's why plumbing codes and water systems call for backflow preventers. [11][12]

Backflow preventer

Also called: backflow prevention assembly, backflow prevention assemblies, backflow device, backflow prevention device

A backflow preventer is any method, device or assembly that stops backflow; Wisconsin's plumbing code defines it as "any generic backflow prevention method, device, or assembly." One example EPA pictures is a double check backflow prevention assembly. Water systems may require customers "to install and maintain backflow prevention assemblies," for example on irrigation systems, and to have them tested and repaired. [11][12]

Backflow tester

Also called: backflow certification, backflow testing, backflow prevention assembly tester

A backflow tester checks that backflow preventers still work. EPA says backflow staff "should be trained and certified in testing backflow prevention assemblies," and that the rules vary from state to state. The ASSE 5110 standard covers "Backflow Prevention Assembly Testers." Some states tie this to a plumbing license: Minnesota, for example, has a backflow prevention rebuilder qualification for licensed master or journeyworker plumbers. [10][12][13]

Building drain

The building drain is the lowest main drain pipe within or under a building. It collects waste from the drains above and carries it out to the building sewer. [11]

Building sewer

Also called: sewer line, sewer lines

The building sewer is the part of the drain system outside the building. It carries waste from the building drain to the public sewer, a septic system or another point of disposal. Some states license workers who install only sewer and water lines, such as Arkansas's restricted water and sewer service line license. [11][15]

C

Cleanout

A cleanout is an opening in a drain pipe that you can get to for clearing clogs; Wisconsin's plumbing code calls it "an accessible opening in a drain system used for the removal of obstructions." When a drain clogs, the cleanout gives a way into the pipe. Texas, for example, registers drain cleaners who install cleanouts and reset P-traps to clear blockages in building drains and sewers. [2][11]

Cross-connection

Also called: cross connection, cross-connection control

EPA defines cross-connections as "actual or potential connections between a potable water supply and nonpotable water plumbing." EPA's examples include private irrigation and fire sprinkler systems connected to the public water system. "Cross-connection control" is the work of finding these links and protecting them with backflow preventers. [11][12]

D

DWV (Drain, waste and vent)

DWV is the part of a plumbing system that takes used water and waste away: the drains from each fixture, the larger pipes they feed, and the vent pipes that let air in so everything drains smoothly. It's the other half of plumbing from the water supply side. Licensing exams cover it; Arkansas's journeyman exam, for example, has you draw a DWV riser diagram in isometric format. [11][14]

F

Fuel gas

Also called: gas piping, gas line, gas lines

Fuel gas is gas burned as fuel, such as natural gas and propane. Gas piping runs from the gas meter to the appliances, such as furnaces and water heaters. Some states require a special license to work on gas lines, and the work follows a fuel gas code such as the International Fuel Gas Code or NFPA 54. [1][20]

G

Gas fitter

Also called: gasfitter, gas fitters, gasfitters

A gas fitter installs and repairs the gas piping that runs from the meter to gas appliances. The District of Columbia, for example, defines a gasfitter as someone who installs, tests or operates gas appliances and piping "from the outlet of the meter set assembly" to the appliances. Rules vary: some states require a special license to work on gas lines, and Arkansas, for example, offers a restricted gas fitter license. [1][15][20]

H

Hydronic heating

Also called: hydronic, hydronics

Hydronic heating warms a building with hot water or steam moving through pipes, instead of air blown through ducts. A boiler heats water "(for steam or hot water) that is distributed via pipes to upright radiators, baseboard convectors, or radiant floor tubing." Some hydronic systems also cool, and ASSE offers a professional certification in "hydronic heating and cooling." [9][17]

I

IAPMO (International Association of Plumbing and Mechanical Officials)

IAPMO is the organization that writes the Uniform Plumbing Code. It was founded in 1926 and focuses on plumbing and mechanical systems. Since 2017 it has also maintained the National Standard Plumbing Code. [4][5]

International Fuel Gas Code

Also called: IFGC

The International Fuel Gas Code is the International Code Council's model code for fuel gas piping and gas-burning appliances. ICC says it is adopted in 41 states, the District of Columbia, Puerto Rico and Guam. It matters to plumbers because many of them also work on gas lines, and some states require a special license for that work. [1][6]

IPC (International Plumbing Code)

The International Plumbing Code is a model plumbing code written by the International Code Council (ICC). "Model" means it does nothing on its own until a state or city adopts it as law. ICC says the IPC is adopted in 37 states, plus Puerto Rico and Guam, and that a new edition is developed every three years. Check which edition your state or exam uses before you buy a code book. [3]

Isometric drawing

Also called: isometric

An isometric drawing is a piping sketch drawn in a standard "isometric format," showing a whole system, such as the drains and vents, in one diagram. Some state plumbing exams include one. Arkansas's journeyman exam, for example, asks you to "draw a DWV riser diagram" for a floor plan "in isometric format," with vents in blue, drains in red and pipe sizes marked. [14]

J

Journeyman plumber

Also called: journey-level plumber, journeyworker plumber

A journeyman plumber has finished an apprenticeship (or the required work hours) and passed the state's licensing exam. The Bureau of Labor Statistics says journey-level plumbers "are qualified to perform tasks independently." Hours vary by state; Texas, for example, requires at least 8,000 hours under a master plumber plus an exam. Some states, such as Minnesota, say "journeyworker." See what is a journeyman. [1][2][13]

L

NFPA 58 (Liquefied Petroleum Gas Code)

NFPA 58, the Liquefied Petroleum Gas Code, covers "the storage, handling, transportation, and use" of LP gas such as propane. In NFPA's words, it applies outside a home, before the final pressure regulator, while NFPA 54 takes over inside. [7]

LP gas

Also called: LP-gas, liquefied petroleum gas

LP gas (liquefied petroleum gas) is a fuel gas that is mostly propane, though it can also contain butane and similar gases. Propane is a byproduct of natural gas processing and oil refining. "It is stored under pressure inside a tank as a colorless, odorless liquid," and it readily evaporates into a gas. The rules for the tank and outside piping are in NFPA 58. [7][21]

M

Master plumber

A master plumber has worked as a journeyman for several years and passed another exam. Texas, for example, requires at least two years as a journeyman (or one year plus an approved training program). Masters may design and supervise plumbing jobs, and some states require master status to get a plumbing contractor license. Compare the two in journeyman vs. master. [1][2]

Medical gas piping

Also called: medical gas, medical gases, med gas

Medical gas piping carries gas and vacuum "used for medical purposes," as in health care facilities. Some states require extra credentials for it. In Texas, only a licensed master or journeyman plumber with a medical gas piping installation endorsement may install it. ASSE also sets qualifications for medical gas workers in its Series 6000 standards; 6010 covers installers. [2][10]

N

NFPA 54 (National Fuel Gas Code)

NFPA 54, the National Fuel Gas Code, comes from the National Fire Protection Association. It covers gas piping and gas appliances. NFPA's fact sheet sums up the split with NFPA 58 as "58 at the Gate, 54 under the Floor": NFPA 54 applies inside a home, after the point of delivery or meter. [7]

National Standard Plumbing Code

Also called: NSPC

The National Standard Plumbing Code is a model plumbing code that the Plumbing-Heating-Cooling Contractors Association created in 1933. Since 2017 it has been maintained by IAPMO. You'll meet it less often than the IPC and UPC; PHCC points buyers in Maryland and New Jersey to their state bookstores for it. [5]

P

P-trap

Also called: trap seal

A trap is a bend in the drain that holds water. In the words of Wisconsin's plumbing code, that water forms "a liquid seal which prevents emission of sewer gases" while still letting wastewater through. It only works if it is properly vented. The P-trap is a common kind; Texas law, for example, mentions removing and resetting p-traps to clear blocked drains. [2][11]

Plumbing code

A plumbing code is a set of rules for installing plumbing safely: pipe sizes, materials, drains, vents, fixtures, water heaters and more. Plumbers "follow state and local building codes," so the code you work under depends on where you work. Most places adopt a model code written by a national group, usually the International Plumbing Code or the Uniform Plumbing Code, and may change parts of it. Texas, for example, has its plumbing board adopt both and lets cities amend them within limits. Apprenticeship classes teach "local plumbing codes and regulations." [1][2]

Plumbing contractor

A plumbing contractor is a business that offers plumbing work to customers. Running your own plumbing business "may require additional licensing," and some states require master plumber status for a plumbing contractor's license. In Minnesota, for example, each contractor names a licensed master plumber as its responsible individual. [1][13]

Plumbing fixture

A plumbing fixture is a receptacle or device connected to the water supply or the drain system, such as a sink, toilet, bathtub or shower. Plumbers "install plumbing fixtures, such as bathtubs and toilets." [1][11]

Plumbing vent

Also called: vent system, vent piping, vent pipe

Wisconsin's plumbing code, for example, defines a vent as "a part of the plumbing system used to equalize pressures and ventilate the system." Vent pipes move air to and from the drain pipes "to protect trap seals from siphonage and back pressure," so the water in each trap stays put and keeps sewer gas out. [11]

PHCC (Plumbing-Heating-Cooling Contractors Association)

PHCC is a national association of plumbing and HVACR (heating, ventilation, air conditioning and refrigeration) businesses, both open shop and union. It traces its history to 1883 and says it set up the framework for the industry's first apprenticeship system. Today it offers education and training to its members, and you'll see PHCC chapters named among plumbing apprenticeship options. It also created the National Standard Plumbing Code. [5][8]

Potable water

Potable (POH-tuh-bul) water is water that is safe to drink. Wisconsin's plumbing code defines it as water that is "Safe for drinking, personal or culinary use" and free of anything that could cause disease. A big part of a plumber's job is keeping potable water pipes separate from dirty water; see cross-connection and backflow. [11]

R

Residential plumber

Also called: residential journeyman plumber, residential master plumber, tradesman plumber-limited

Some states offer a plumber license limited to homes. Utah's residential journeyman plumber, for example, needs 6,000 hours as a licensed apprentice plus a 3-year approved school program (or 12,000 hours of experience) and the residential exams. Texas has a "tradesman plumber-limited" license for one- and two-family homes, reachable with 4,000 hours as an apprentice. [2][22]

Restricted plumbing license

Also called: restricted plumber, restricted master plumber, restricted journeyworker, limited plumbing license

A restricted (or limited) plumbing license allows only part of the trade. Arkansas law, for example, defines a restricted plumber as someone qualified for "building water or sewer lines or other special phases of plumbing," and issues restricted licenses such as gas fitter and water and sewer service line installation. Minnesota's restricted master and journeyworker licenses work only in cities and towns of 5,000 people or fewer. [15][23]

Rough-in

Rough-in is the stage when the pipes are in place but walls and floors are still open and the fixtures aren't set yet. Codes usually require a rough-in inspection at this point. Wisconsin's code, for example, says it is made "when the plumbing system is roughed-in and before fixtures are set," and the work can't be "closed in, concealed, or covered" until the inspector approves it. [16]

S

Septic system

Also called: septic tank

A septic system treats wastewater on the property instead of sending it to a city sewer. EPA says a typical system has "a septic tank and a drainfield." Solids settle in the buried tank, and the liquid flows out through perforated pipes into the soil. The BLS notes that plumbers "also help maintain septic systems." [1][18]

Sprinkler fitter

Also called: sprinklerfitter, fire sprinkler fitter

A sprinkler fitter installs fire sprinkler systems. The Bureau of Labor Statistics' profile of plumbers, pipefitters and steamfitters notes that some fitters "specialize as gasfitters or sprinklerfitters," and that building codes requiring fire suppression systems drive demand for sprinkler fitters. [1]

U

UPC (Uniform Plumbing Code)

The Uniform Plumbing Code is a model plumbing code published by IAPMO. Like the IPC, it becomes law only where a state or city adopts it. IAPMO lists Los Angeles, Houston, Minneapolis, Seattle and Portland among the cities that use it. The current edition is the 2024 UPC, so check which edition your state or exam uses. [4]

W

Water conditioning

Water conditioning means installing and servicing water treatment equipment: devices that remove contaminants from water or add treatment chemicals to it. A few states license it as its own specialty. In Minnesota, only licensed plumbers or water conditioning masters and journeyworkers may do this work, and businesses need a water conditioning contractor license. [11][19]

Water heater

A water heater heats water for the faucets, showers and appliances in a building. Most homes use a storage tank heater fueled by natural gas, propane, fuel oil or electricity; tankless (on-demand) heaters heat water directly without a storage tank. Installing water heaters is regular plumbing work, and gas water heaters are hooked up to gas piping. [1][11][17]

Water service

Also called: water service line, water service lines

The water service is the pipe that brings water from the water main (or a private well) to the building. Inside, the pipes that carry water to each fixture are the water distribution system. Wisconsin's plumbing code, for example, draws the line between the two at the building's main shutoff valve. [11]