If I untwist one of the Oatey Air Admittance valves under either the main kitchen sink or the island sink the sink drains normally. Otherwise I hear gurgling, usually in the island sink. I put a plastic bag over the AAV pipe and unscrewed the AAV, the bag filled with air when I ran the sink. Isn't an AAV supposed to allow air in, not out? What is the likely problem?
Mark
Mark