Once you understand the basic theories behind moving water through a home and get to know the basic materials and materials handling techniques, you will be able to tackle just about any plumbing repair or project with confidence.
In a nutshell, here’s how plumbing works:
Water is brought into the home under pressure through a metered water main. The main has connected to supply pipes, usually ¾-inches in diameter copper. The supply pipes run in parallel pairs throughout your home. One takes a detour at the water heater, then rejoins the cold water supply pipe to carry hot water to sinks, bath tubs and showers. The supply pipes typically run through the joist and wall cavities, passing through floors or walls near plumbing fixtures, where they are connected to the fixtures with water supply lines, usually ½ inches copper or plastic. Usually several plumbing fixtures are services by one loop of the supply pipes.
Throughout the network of pipes and at each plumbing fixture, shut off valves are inserted into the supply lines so the water flow can be stopped if needed. The water leaves the network through a network of drains that for the drain/waste/vent (DWV) system. Individual fixtures are connected to a vertical main drain stack via branch drains that run at a slight downward slope through floor and wall cavities. The main stack connects directly to the sewer or septic line outside the home.
To prevent pressure and gas built up, the entire DWV system is connected to a network of vent pipes that also work their way to the main stack, which rises all the way through the building and exits through the roof in the form of a roof vent.
This only briefly describes how the plumbing system works. And though it may seem a common knowledge to a plumber most people have very little to no knowledge about it at all.