When your kitchen sink gurgles or the water drains slowly, install an Air Admittance Valves (AAV) to fix the problem. Air Admittance Valves are accepted for single and multi-family residential construction and remodelling by International Residential Code (IRC) and by American Society of Sanitation Engineers (ASSE). Some local codes are unsure about how well the air admittance valve works, despite the code listings them as acceptable, they are reluctant to accept the air admittance valves. Air admittance valves are air vents that are installed under the sink to vent it without an outside vent pipe. The AAV is a one-way valve that allows air to enter the drain when the sink empties. Gravity closes the valve when the sink is done draining and preventing gas from the sewer escaping into the home. They are relatively easy to install.
Install the sink drain and trap as the manufacturer suggests for the style you have purchased. At the end of the trap, cut and install a 1 1/2 inch pipe, 12 inches long angled toward the main sewer drain the sink drain will connect to. Use plumbing PVC primer and PVC cement when connecting the pipes to the main drain.
Install a 1 1/2 inch sanitary tee with the sweep on top, going towards the main drain on to the pipe you connected to the trap. Measure the distance from the tee to the main drain. Cut a piece of 1 1/2 inch pipe to go from the tee to the main drain and install. More fittings may be needed to connect the drain to the main drain depending on the plumbing situation.
Measure the distance between the counter top and the outside of the tee to get the measurement for the pipe between the tee and the air admittance valve. The air admittance valve will need to be 4 inches above the beginning of the sink drain. The higher the valve the better.
Figure out the length of pipe between the air admittance valve and the tee: The air admittance valve is 2 5/8 inches long and you will want to leave 2 inches of space between the counter and the air admittance valve, so deduct 4 5/8 inches off the measurement between the counter top and the outside of the tee to allow room for the valve. Cut a piece of 1 1/2 inch PVC pipe, connect the pipe to the tee and connect a 1 1/2 inch female adaptor to the end of the pipe.
Screw the air admittance valve on to the female adaptor, use threaded seal tape on the treads of the valve.
Air admittance valves need to be installed higher than the fixture, get it as high above the counter top as possible. Do not use pipe dope sealants on the air admittance valve.
Check your local codes before installing an air admittance valve.