Drain, Waste & Vent Plumbing Systems

In this section of Hometips for Home Improvement, I explain all about Drain, Waste & Vent Plumbing Systems. Drain, Waste & Vent Plumbing System or Drain-Waste-Vent (DWV) need to be properly planned so that waste water and sewer gasses can be drained out properly without getting clogged.

What is drain-waste-vent (DWV) system?

Well, the plumbing system of the house with large-diameter pipes that carries water and waste to a sewer line or septic tank is called the drain-waste-vent (DWV) system. The name itself consists of three words – Drain Line, Waste Line and the Vent Line. The drain lines collect water from sinks, showers, and tubs; the waste lines carry waste from toilets; and vent lines exhaust sewer gasses and provide the necessary air pressure to allow wastes to flow freely. All these drain and waste lines must always slope slightly downward from the fixture toward the sewer or septic system. Water and wastes are carried by gravity.

The drainage pipes used in the system are large in diameter ranging from 1 1/4 inches to 4 inches. Large diameter of the pipes minimizes the possibility of any unwanted blockages or clogging. Pipes for the main soil stack for toilets are normally a 4-inch in diameter while pipes in the showers are normally of 2-inch in diameter.

Lavatories, sinks, bathtubs, and laundry tubs may have pipes of diameter 1 1/4-inch to 2-inch. Most of these drain piping is cast iron, copper or durable plastic. Some older homes even have pipes made of lead and galvanized iron.

In order to ensure proper and safe operation and functioning of the system one must ensure that each drain is served by a vent line that carries sewer gasses out through the roof. One can also connect several vents together that can be joined to the soil stack as long as there is no drain above the connection point. Vents may also pass through the roof on their own.

All waste lines should have cleanouts at locations that are easily accessible. A cleanout is basically a simple Y-shaped fitting in the line that is capped off. In case of any blockage a plumber can easily to snake out the line.

Drains should be protected by traps to prevent sewer gasses and odors from entering the house. A trap is basically a curved section of drain pipe that fills up with water, providing a seal.

Drains penetrating a wall have a P trap. Drains that go through the floor have an S trap. The water held by the trap is replaced each time the fixture is used.

I hope this article helped you in understanding the Drain, Waste & Vent Plumbing System.