The plumbing system of a building functions to provide freshwater and to remove waste water.

The part of the plumbing system that removes waste water is dependent on drain traps and vents to maintain water flow. Drain plumbing runs from all the facilities within a building that produce waste water (including sinks, toilets, washing machines etc) and all join in one waste pipe before leaving the building. The plumbing in waste pipes is usually made of hard plastic PVC although some buildings may still have cast iron waste plumbing.

The most important part of wast plumbing is the soil stack, which is a series of pipes that connects to the waste line that leaves the building. The top end of the pipe opens to the roof and allows the inflow of air through the plumbing system to enhance the flow of water and prevent clogging.

Another important component of waste plumbing are traps which are installed directly below drains. The S shape of the trap blocks septic gases from travelling back up the plumbing from the septic tank by blocking a small amount of water in the curve thus preventing the movement of gases.

Freshwater is supplied through copper plumbing at high pressure to enable the water to be moved throughout the home. Because these pipes are held at pressure, all pipes are fitted with shut off valves which should be utilised in the case of a plumbing emergency to prevent expensive water damage to a building or home.

Any part of a plumbing system that bridges between freshwater supply and waste water drainage is referred to as a fixture. For example toilets, sinks and washing machines are fixtures. All fixtures should also have their own supply shut off valve to allow repairs to be made to the fixture or surrounding plumbing.