Most home plumbing systems are composed of three things: the water supply system, the fixtures and appliances, and the drainage system. Water enter a home through a main supply line, either a municipal water company or a private well. If it comes from a municipal source, it must first pass through a meter which measures the amount of water used.

Once the water from the main supply enters the house, the branch line splits off and joins the water heater. From there, the hot and cold water lines run parallel to each other to all the fixtures and appliances in the house. Once the water becomes waste, it runs into a trap and then into the drain system which works totally by gravity. Waste water flows downhill through a series of large diameter drain pipes, which are attached to a system of vent pipes. Vent pipes permit air to enter the system through a roof vent. This fresh air prevents suction that would stop the free flow of drain water.

All sewage will eventually reach the waste and vent stack. The waste water flows in the sewer line and exits the house via a municipal sewage system or a private septic tank. In the meantime, sewer gas rises through the vent and escapes through the roof vent, thus rendering it harmless.

Most of the pipes in modern homes are made of copper but plastic is becoming more popular. Homes build before the 1950's usually had pipes that were made of galvanized iron. Iron pipes can lead to water that looks rusty when it first comes through the fixtures.

Most pipes in the drainage waste system is made of plastic or cast iron. They can be one and a quarter inches to four inches in diameter to allow easy passage of waste water through the pipes. Lead pipes are no longer used in home plumbing, though for the waste drainage system they do not pose a health hazard. Slope is an important factor in the waste drainage system, and each section must have the proper degree of slope to allow the system to function as intended, working with gravity to remove the wastes.