[SOLVED] Hello, My girlfriend lives in the country in an old house whose plumbing was remoldeled 30 years ago. All the new plumbing fixtures are located within 15 feet of the main sanitary drain that connects to the outdoor septic system and these drain well. However there is a kitchen sink located 57 feet from the main sanitary drain which is giving us a problem. This 57 foot drain is composed of 2 vertical feet of 1.5" pipe under the sink to the basement, 15 feet of 1.5"pipe @ 2% slope, a backflow valve, 2 feet of 1.5" pipe @ 2% slope, 8 feet of 2" pipe @ 2% with two 90 degree shallow elbows, and finally 30 feet of 2" pipe @ 1% slope with two 45 degree elbows. Unfortunately when the kitchen was remodeled, no ventilation stack was installed for the kitchen sink due to the exterior walls being made of cement block. Since a few weeks the kitchen sink was draining slowly, so I ran a fish through all of the 2" pipe and found no blockage. Today I installed an Air Admittance Valve under the kitchen sink hoping that it would increase the drain flow. After I filled the sink half full and pulled the stopper, it still drained very slowly. But as soon as I unscrewed the Oatey AAV from its mating collar, the sink quickly drained, albeit with some water over flowing out of the fitting where the AAV was previously connected. I placed a plastic bag over the open fitting where the AAV was and as I drained the sink a second time, the bag filled up with air. Conclusion: In order for the kitchen sink to drain well, any trapped air in the 57 feet of sloped drain pipe needs to evacuate in order to let the sink water take its place. In my situation, this air cannot evecuate easily unless I create a vent under the kitchen sink with no AAV attached. Sewer gases are not a problem for the kitchen sink because the flap on the backflow valve in the drain path is sealing cleanly. My only risk is if I fill up the kitchen sink and pull the stopper, then sink water will finds its way back to the fitting for the missing AAV and overflow into the under sink cabinet. Just running water into the sink with no stopper works well. What I need is an Air Expulsion Valve which would allow air to flow in both directions but block water from escaping through the valve. Such a valve could be made of a cage with a ping-pong ball which would float upwards and seal off the device. Otherwise I would have to raise my new under sink vent so that the top of this vent would be above the highest level of water in the sink. That would require extending the vent through a new hole drilled into the kitchen counter top. It is easy to suggest that if I increase the slope of my 30 feet section of 2" pipe from 1% to 2%, then all my problems would be solved, but I`m not so sure. Any other suggestions would be appreciated. Thanks for reading.