Galley Sink Vent issue
Had smell coming from under galley sink, replaced vent, old one looked pretty gummed up and dirty. Now the sink will not drain unless I loosen the vent, when I loosen it will hiss and sink will drain ...
Forum Discussion
westend wrote:
An air admittance fitting under the sink should not hold drain pressure,i.e. if it hisses when you twist it partially off, it is not working correctly.
Actually, I disagree with this statement. Holding tank pressure is EXACTLY what the AAV should do. It is supposed to let air INTO the tank, and keep air (and smells) from exiting the tank. What is supposed to let air (and smells) out of the tank is the roof vent, which is exactly why everyone keeps saying to check to see if it is blocked. If you are getting hissing air (and smells) when you loosen the AAV, the tank is pressurized meaning the roof vent is not working.
Another cause for this, rarer than merely a blocked vent, is the vent pipe has come unfastened and slipped down into the tank. That means the bottom of the roof vent pipe is under the water line of the tank, and not venting.
