The drain, waste and vent (DWV) system is made of large-diameter pipes that carry water and wastes to the sewer line or septic tank. As the name implies, this system has three important components: drain lines collect water from sinks, showers and tubs; waste lines carry wastes from toilets; and vent lines exhuast sewer gases and provide the necessary air pressure to allow wastes to flow freely.

All drain and waste lines slope slightly downward from the fixture toward the sewer or septic system, and the water and wastes move by simple gravity. The pipes are large in diameter -- typically 1 1/4 inches to 4 inches -- to prevent blockages. The main soil stack for toilets is normally a four-inch pipe; showers usually have two-inch pipe drains. Sinks, lavatories, bathtubs and laundry tubs may be served by 1 1/4-inch to two-inch pipes. Most drain piping today is cast iron, plastic, or in some houses, copper. Some vent pipes are made of galvanized iron.

A cleanout should be located in all waste lines at easily accessible locations. A cleanout is simply a Y-shaped fitting that is capped off. If a blockage occurs, this is the easiest place for a plumber to clear, or "snake out" the line.

Copyright Don Vandervort