Galley Sink Vent issue

westend wrote:

Bobbo wrote:
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.

Hey, I'm not a technical writer for a plumbing distributor. Both of you guys would agree with the basic stuff I wrote. Maybe I should have written "drain pressure/vacuum" instead of "drain pressure" and explained that a single pipe can handle two drains. The information remains the same but I'm about done being scolded for not appealing to the sensitivities of some readers.

Instead of scolding, help the guy out.

I did help the OP out. Read the last sentence of my quote above.

Also, you may not be a technical writer, but misinformation still needs to be corrected.

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.

This statement is just plain wrong. If it hisses when you twist off the AAV, it is the roof vent that is not working correctly.

And, in a section that you did NOT quote, I also pointed out that tanks may "Y" into the same vent so the number of vent pipes through the roof may not match the number of tanks.

Bobbo wrote:
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: