Drainage, Waste & Vent (DWV) Systems

A drainage, waste, and vent system (DWV) is a network of large pipes that take the water used in sinks, toilets, and tubs out of the house into a sewer or septic system.


How Drainage, Waste and Vent (DWV) Systems Work

As the water builds up, larger pipes are necessary to handle the volume, so that it can drain quickly. There also needs to be space for the build up of air and gas that comes with the waste disposal. Once the waste is deposited in the sewer, it begins to decompose, which produces noxious gases. Therefore, a trap on the drainage system is needed so that those gases do not escape back into the house.

Drainage, Waste and Vent (DWV) System Traps

The trap is usually a U-shaped piece of pipe that holds a small amount of water, which acts as a barrier between the house and the sewer system. DWV pipes do not sustain much pressure, so it can be made from a variety of materials, including plastic.

Drainage, Waste and Vent (DWV) System Venting

Venting provides an efficient way for the gas pressure to escape. Every appliance is connected to a large drain pipe, which is connected to a venting pipe that eventually extends through the roof of the house, providing another way for the gas to leave the drainage system. The vent provides a means for the air to enter the system, which is necessary for the water to flow out. Adequate ventilation is essential to the smooth operation of the plumbing system.

As water displaces air, there is a build up of pressure, which is released by proper venting. The drainage system has to be designed to maximize drainage. Hence, they need to work with gravity and run vertically, or at least slope adequately.

Vent Pipe Connections

As the network of pipes proceeds, it reaches the waste stack, a large collecting drainage pipe that is connected to the sewer or septic system outside the house. At the far end of the waste stack is the roof vent, coming from a series of vent pipes.

The vent pipes from appliances in the lower portion of the house connect to those in the upper part such as upstairs bathrooms, and depending on how many appliances there are in the house, is attached to one or more roof vents.

There are books and Internet sites that explain how to install such drainage, waste, and vent systems with step-by-step instructions, lists of materials needed, pictures, and what NOT to do!