Venting Problems?

[PT100]

We have a modular home with air admittance valves under all the sinks and one vent pipe through the roof. The toliets were not flushing as they should. I discovered that they would flush when any one of the air admittance valves were removed, so I replaced the air admittance valves under all the sinks. The toliets seemed to work a little better for a day or two, but are now back to not flushing everytime. I checked the pipe in the roof and there is some type of flap or something in it. Could the problem be with the roof vent? Thanks for any suggestions.

[Terry]

I'm not aware of a purpose for a flap in the main vent.

I would say to remove it.
For your AAV's to work, there must be at least one main vent that is open.

[Gary Swart]

Perhaps the flap in the main vent was put there to keep small critters out. Remove it and see what happens. If that fixes the problem, but you are worried about the pipe being open, you can put a piece of hardware cloth over the opening.