How to Install a Plumbing Auto Vent

All plumbing systems require an air inlet so that the liquid and waste that are placed into a drain will flow downward. Without an air vent, the negative air pressure inside the pipe would create backups. While the most common form of air vent is the vent stack that runs from the pipes to the roof, automatic air vents do not require pipes sticking out of the roof. Instead, these devices attach directly to a P-trap and allow air to enter the line. At the same time, a small check valve inside the vents prevents harmful gases from escaping from the pipe.

Pliers

Instructions

- 1
  Remove the cap on top of the three-way T-fitting just behind the P-trap under the sink or other fixture. The cap removes by unscrewing the square knob on the top of the fitting. You may need to use pliers to remove the cap. This will expose 1 1/2-inch female pipe threads.
- 2
  Place the male threads on the bottom of the auto air vent, or air admittance valve, into the hole on the T-fitting.
- 3
  Tighten the valve into the T-fitting by turning it clockwise by hand until snug.
- 4
  Turn on the water in the sink or other fixture and allow it to run for about three minutes. During this time, place your hand on top of the auto vent and feel for a slight air rush at the valve opening. The air should run into the pipe and allow the water to drain smoothly with no backup of water.

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