Vents are the pipes (about 12” high) that stick out of your roof. Vents are necessary to vent sewer gasses outside of the home. You can think of a vent pipe like a straw. When you put your thumb over the end of a straw, you can pull liquid up from the cup. What happens when you remove your thumb? The liquid drains out and the straw fills with air. Similarly, when liquid goes down a pipe, air needs to follow it. This air is pulled from the vent pipe. Without a vent pipe, the liquid will try to pull air through the P-traps on plumbing fixtures such as your tub and sink! If this happens, you’ll know from the smell! Likewise, without a vent, draining one fixture may cause another fixture in the house to back up!