A air admittance valve is an inline valve which allows air into a drain line to help water drain quickly. An under-sink installation of the air admittance valve allows air to equalize the pressure inside the drain without allowing sewer gases to escape the valve and to the home. You can install an air admittance valve under the kitchen sink in about an hour using some common hand tools.
Loosen the couplers holding the P-trap and female trap adapter on the sink drain under the kitchen sink with a massive group of slip-joint pliers. Place the P-trap and trap adapter aside.
Cut the 1 1/2-inch drain line to the wall just behind the coupler that is glued to the pipe using a hacksaw. Eliminate the cut off section and place it apart. Clean out the burrs on the drain tube in the wall by hand.
Prime the drain tube and the lower female end of a Wye connector, then apply a layer of glue into the pipe and attach the female end of the Wye connector, with the split pipe of the Wye facing upwards.
Thread a air admittance valve on a female coupler. Position the coupler and flashlights over the split pipe of the Wye connector, and assess the distance between the top of the air admittance valve and the bottom of the sink using a tape measure. Cut a bit of 1 1/2-inch PVC pipe into this span.
Apply PVC primer to a end of the pipe section and also the female coupler connected to the air admittance valve, then apply glue to one of the primed sections and insert the pipe to the female coupler. Prime the opposite end of the pipe section and the top split pipe of the Wye, then glue among both primed areas and add the pipe to the Wye.
Prime the open end of the Wye and the suggestion of a female trap adapter, then glue and insert the adapter to the Wye.
Connect the trap adapter and P-trap between the Wye and the sink’s tailpiece and tighten the couplers using the slip-joint pliers.
Turn on the faucet and analyze the drain.