Step 2 · Mark the Cut Location
Identify the correct location for the AAV. It must be installed on the horizontal drain arm between the P-trap and the wall connection. Crucially, the valve must be positioned at least 4 inches above the top of the horizontal drain arm. It also needs to be as high as practically possible under the sink, but still below the flood-level rim of the sink itself. Use a measuring tape and a marker to mark the section of the horizontal pipe where you will cut to install the new sanitary tee fitting. Ensure the marked section is long enough to accommodate the body of the tee.