oder problem

Currently have the same problem. Someone suggested the air admittance valve and if that is the case we would be smelling the gray tank and not the black so I suppose this is a possibility. I have heard the gray can smell just as bad as the black. MH has been winterized now so won't be able to investigate further till spring. We also had an issue when new where the rubber coupler between the gate valve and the macerator came loose. When to dump and got a nasty surprise. Still trying to get the smell out from that incident. Noticed the other day that it is trying to slip off again so I see another repair on this in the future. Another suspect was having one of the vents open while traveling and it sucking in fumes but upon further testing I don't think that is the problem.