Understanding The Drain – Waste – Vent System at Home (DWV)

The Drain-Waste-Vent (DWV) pipes carry waste and water out of the house without gasses or tinkles.

An image demonstrating the drain waste vent system

The main piece of a DWV system is the stack, normally a pipe 3 or 4 inches in diameter that runs straight up through the roof. Water travels sliding through the stacks to the main drain line, which leads to the municipal sewage system or to a septic system.

In older homes the main drain may be made of clay pipe or other porous material. Tree roots sometimes work their way into the main line, causing wastewater to back up into the house. If that is the case the solution is to call a company that specializes in auguring main lines. Drain stacks in older homes are often made of cast iron, which rusts through after 80 years actually the new homes instead use plastic pipe for stacks and branch drains.

Drainpipes must be leaned generally about 1/4 inch per foot, so water can run freely through them. Codes require special fittings that make sweeping, rather than abrupt, turns so waste does not get stocked in the pipes. Drainpipes often have cleanouts these are some places where a plug can be temporarily removed so the pipes can be equipped to clear a clog. Vent pipes also carry odors out of the house.

There are some other drainpipes:

  • Secondary stack: A 2 or 3 inches in diameter pipe that serves a branch of the system.
  • Branch Drainpipes: Smaller diameter pipes, normally 1-1/2 or 2 inches that carry water from specific fixture to a stack.

Another aspect to consider from the DWV system is the vent pipes those allow water to flow smoothly without gurgling. Normally Vent pipes extend from the drainpipes up through the roof to provide that passage. Vent pipes also carry odors out of the house.

The drainpipe for each plumbing fixture must be connected to a vent that supplies the pipe with air from the outside however in some cases the drainpipe is connected directly to a main or secondary stack pipe, which travels straight up through the roof.

Plumbing codes strictly recommend where vent pipes can connect to the stack and how far they should travel. In most cases a damp section of a pipe frequently the part that carries wastewater cannot be used as a vent, even if it is usually dry.

If your drainpipes gurgle when you run water in a sink or flush a toilet, call a professional plumber for an inspection. A vent may be stopped up and need clearing. Or the plumbing may be incorrect, and you may need a new vent line.

Never install or replace a DWV pipe without consulting a building inspector. These pipes must be installed according to precise specifications.

For more information about your DWV contact Benjamin Franklin Plumbing® of Port St. Lucie. The specialist’s plumber in the Treasure Coasts and Palm City Area (772) 205-3132