Hello everyone, not trying to beat a dead horse here but did someone come up with a solution to this problem? LBVS. I have a keystone everest 323k I have two Air conditioning units installed in my fifth wheel like most do. The main in the lower living room half if a central AC with ductwork throughout the roof also leading to bedroom upstairs. The upstairs bedroom also has a independent older model AC unit just for bedroom I presume when the central AC just isn't quite enough to cool off upstairs as well. So if my AC upstairs is not running and I flush my toilet no issues with smell. If my upstairs AC is running and I flush toilet now I have sewer smell. I treat my tank almost weekly I know my vent to black tank is open because I've opened the cover on top and ran water down the vent into the black to ensure it was open. I get that hypothetically inside air is supposed to stay inside air and outside air outside air but clearly that's not happening here. Some how the vent smell from black tank when flushing is getting into bedroom AC. It doesn't smell any other time unless you flush toilet. Also to clarify there's no smell coming directly up from my toilet either I clean that weekly as well. Plumbing and seal is also good as I had a plumber add new seal for me. So I've checked all my boxes. Any resolutions other then just dealing with it or replacing bedroom AC. Also the living room AC is not affected by this whatsoever. This is only when the bedroom AC is on. Not when it's off.