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How to Install an Air Admittance Valve Under the Kitchen Sink

When installing a kitchen sink, you need an air admittance valve to let air into the drain line when water is flushed down it. An air admittance valve is a one-way valve that lets air in, but not out, so sewer and drain gases do not come through. Putting the valve on the drain line involves a few extra steps but it is something anyone with some experience running pipe can master. The valve connects directly to the drain line under your sink.

Things You'll Need

  • P-trap and fittings (lock nuts and washers are included with most P-traps)
  • T-fitting
  • PVC cement
  • Pipe saw
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    • 1

      Connect the P-trap to the sink drain tail pipe, by sliding a lock nut and compression washer up and over the tail pipe and tightening the lock nut on the threads of the P-trap.

    • 2

      Install a T-fitting on the other side (outlet side) of the P-trap pipe between the P-trap and the home's main drain pipe. If necessary, cut the existing drain line using a pipe saw. Connect the T-fitting to the drain pipe and P-trap with PVC cement. Note, if your air admittance valve comes with its own T-fitting, meaning is already it connected to a T-fitting, skip this step and simply install it between the P-trap and home's main drain line.

    • 3

      Coat the air admittance valve with PVC cement and push the air admittance valve into the T-fitting.

    • 4

      Allow between 4 and 8 hours of drying time, or as indicated on your PVC cement instructions, before using the drain.