2 air flappers

Well according to Winnebago what I am looking at are the relief valves for the rear height leveling air bags. Next time I'm by the MH I'll see if I pinch the rubber will air come out.

This a really wild guess, but the OP's RV tanks may be somehow warm-air heated by the RV's propane furnace. The flaps MAY BE for letting the warm air exhaust to the outside after it has circulated around the tanks.

Hi Rich,

I never heard of waste tank flappers. I wonder if your flappers are waste tank heaters or tank insulation that has come loose. Tank heaters are very thin sheets that adhere to the bottom of the tanks. Tank insulation is usually thin silver foil finished material, completely wrapping the tank. The tank heaters would be directly on the bottom of each tank and the insulation covering both.

I agree, pictures would probably help. Is this by the front bumper or the back bumper?

One possibility that comes to mind may be leveling jacks with feet that look like flappers.

Photos might help