When you talk about a sink vent you can actually be talking about two different things. In the world of plumbing, vents are needed for aiding in draining and to keep sinks from overflowing. Here are is a quick rundown of the different definitions of what a sink vent is.
Needed Venting for Draining Waste Water
If you look at the roof line of a home you will notice PVC pipes sticking up in various places. There are called vent pipes. They are connected to different fixtures, mainly bathroom fixtures, and help with the drainage of waste water. The open airway gives gravity a helping hand is pushing water down the pipes. All drains must be tied into a vent pipe for effective draining. A sink vent is one where the sink is tied into the main drainage vent pipe.
Needed to Stop Overflow of Water
Another definition of what a sink vent is, and what it does, is that it is a small vent near the top of the sink that will stop water from overflowing the lip and flooding onto the floor. It is usually situated on the front of the sink at the top. It is connected to a small pipe that flows into the drain pipe.