Why does a plumbing system need a vent?

A plumbing system vent does just that: it “vents” the plumbing system in your home. A vent will look like pipes sticking out of your roof and are about 12” high. This vent allows sewer gases to be vented outside the home. Another function of the vent is that when a liquid goes down a pipe air must follow it. Without vents, draining one fixture may cause another fixture in the house to back up. A waste and vent system should keep sewer gas out of the home and drain every fixture well.