Vent systems maintain neutral air pressure in the drains, allowing free flow of water and sewage down drains and through waste pipes by gravity. All plumbing waste fixtures use venting to prevent sewer gases from leaking into the house.

The venting system, or plumbing vents, consists of a number of pipes leading from waste pipes to the outdoors, usually through the roof. Vents provide a means to release sewer gases outside instead of inside the facility. Vents also admit oxygen to the waste system to allow aerobic sewage digestion, and to discourage noxious anaerobic decomposition. Vents provide a way to equalize the pressure on both sides of a trap, thereby allowing the trap to hold the water which is needed to maintain effectiveness of the trap, and avoiding “trap suckout” which otherwise might occur

Needless to say, without an effective, operational venting system there cannot be a proficient and operational sewer plumbing system.