The water supply system brings cold water into the home under pressure. The water is piped in through a main supply line, usually 1" to 1 1/2" in diameter, from either a well, spring or municipal water supply. If the home has a water filtration or softening system it is most effective when positioned close to the point where the water supply enters the home. After entering the home, some of the water is immediately diverted to the water heater. At this point the hot and cold branch lines, usually from 1/2" to 1" in diameter, are run to stub outs for the various fixtures throughout the home. Small supply lines, usually 3/8" in diameter, are used to carry water from the stub outs to the to the fixtures.
Drain, Waste and Vent System (DWV)
After it is used, water is carried out of the home by gravity through pipes ranging in size from 1 1/4" to 4" in diameter. The size of the drainpipe depends on the size of the fixture, with lager fixtures having larger drainpipes. Each fixture drain has a trap. Some traps are built into the fixture as in a toilet, others are made from curved sections of drainpipe. Traps hold a small column of water that acts a seal to keep sewage gasses from backing up into the home. Fixture drains also have vents that relieve pressure and allow water to flow out freely. Each vent connects to the main vent stack that exits through the roof of the home.
Note that in the virtual plumbing system, the tub drain does not vent in the same manner as the other fixtures. The main drainpipe serves as a vent for the tub in conjunction with the vent for the lavatory. This type of vent is called a wet vent. If you plan to install a fixture using a wet vent system, contact your local coding authorities or a plumber to determine what size pipe you need and how far the fixture can be from the drain/vent pipe.
Cleanouts give you easy access to the DWV system without cutting pipe. Cleanouts are normally installed at the ends of horizontal drain runs and near the point where the main drain or sewer line exits the home.