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Drain, Waste & Vent Plumbing

by Don Vandervort, © HomeTips

The system of large-diameter pipes that carries water and wastes to the sewer line or septic tank is called the drain-waste-vent, or DWV, system.

As its 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 exhaust sewer gases and provide the necessary air pressure to allow wastes to flow freely.

drain waste vent plumbing diagramAll drain and waste lines slope slightly downward from the fixture toward the sewer or septic system. Water and wastes are carried by simple gravity. The pipes are large in diameter—typically 1 1/4 inches to 4 inches—to minimize the possibility of blockages. The main soil stack for toilets is normally a 4-inch pipe; showers usually have 2-inch pipe drains. Sinks, lavatories, bathtubs, and laundry tubs may be served by 1 1/4-inch to 2-inch pipes.

Though older homes may have pipes made of lead, most drain piping is cast iron, plastic, or, in some cases, copper. Some vent pipes are galvanized iron.

To operate properly and safely, each drain must be served by a vent line that carries sewer gases out through the roof. Several vents may be connected together and joined to the soil stack as long as there is no drain above the connection point. Or vents may pass through the roof on their own.

All waste lines should have cleanouts at easily accessible locations. A cleanout is simply a Y-shaped fitting in the line that is capped off. If a blockage occurs, this is the easiest place for a plumber to snake out the line.

To get free recommendations for top-rated local contractors, call the most reliable and comprehensive referral service, HomeAdvisor, at 866-350-2983 (toll free).

© 1997–2011, Don Vandervort, All rights reserved.

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