Galley Sink Vent issue

See if there are any back ABS pipe running from the bottom of a closet to the ceiling. That will be a tank vent going to the roof.

Mark Heron wrote:
I have only been on my roof twice and I don't remember seeing a vent, I'm guessing there must be one, no way there are 3 up there.

I agree that you may have just 1 or 2 vents through the roof, with "Y" connections to the other tanks, if they are close together.

Most of the vents look like this:

joebedford wrote:

westend wrote:
All of your tanks should have a vertical vent that exits the roof.

Buzzer! Nope!

I think you need to elaborate a little more. Every tank must be vented, although not every tank necessarily needs its very own dedicated vent.

I suspect a vent issue more than the AAV under the sink.

Mark Heron wrote:
I have only been on my roof twice and I don't remember seeing a vent, I'm guessing there must be one, no way there are 3 up there.

Nearby tanks can share a vent. At some point each vent line could go into a wye and only have one vent termination through the roof.

I have only been on my roof twice and I don't remember seeing a vent, I'm guessing there must be one, no way there are 3 up there.

westend wrote:
All of your tanks should have a vertical vent that exits the roof.

Buzzer! Nope!

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.

All of your tanks should have a vertical vent that exits the roof. Identify which vent pipe services the galley sink and make sure it is not blocked.

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.

I replaced both at the same time even though I was not having a problem in bathroom. Also I should have stated that I have 3 waste tank tanks, black, grey and galley.

Did you check your roof vent to the grey water tank it could be plugged? It could be plugged.
Is there a similar vent under the bathroom sink? Can you switch them and see what happens?