How to Install a Vent Under a Double Sink

A double sink requires similar venting to a single sink because both drain water in the same way. The only difference is, a double sink has two sink bowls instead of one. Each needs a vent -- or air admittance valve, as they're often called -- to drain water properly. These vents let air flow into the drain pipe lines as water passes through, balancing the negative pressure occurring when water drains through the pipe. Installation only requires the most basic plumbing skills.

T-fitting (or air vent with a T-fitting attached)
Pipe saw
PVC cement

Instructions

- 1
  Locate a suitable position for the air vent on the drain line. Usually, since there are two drains on a double sink, the best location is on the home's main drain line, near the wall and behind the point at which it connects to both sink drain pipes.
- 2
  Cut out a 3-inch section of pipe -- or enough to allow the insertion of the air vent's T-fitting -- from the drain pipe at the point you chose in the previous step, with a pipe saw.
- 3
  Cover the ends of a T-fitting in PVC cement and install it where you cut out the section of pipe.
- 4
  Install the air vent on the top outlet of the T-fitting after coating its edges with PVC cement. If your air vent comes with a T-fitting, you don't need to perform this step; simply install the vent and T-fitting together.
- 5
  Let the PVC cement dry for up to eight hours, or as your cement manufacturer recommends, before running any water in the sink.

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