[Cheif 2]

I hope you are not leaving the black tank valve open all the time. That will cause you considerable headaches soon when the waste material hardens in the tank. Something to check is the drain for the washer. If you have no water in the p-trap you will get odors. As mentioned before the vacuum breaks going bad could be a cause. When I purchased my first 5'r I thought I was doing a great job of flushing the black tank until I purchased a clear elbow and found out how poorly I was doing it. If you do not flush the black tank sufficiently you will have odor problems. If you do not use sufficient water when flushing the bowl after using it you will have odor problems. Another possibility is that with leaving the grey water valve open you are not getting a good "flush" of food particles from the tank. If the previous owner did the same you may have "rotting" food odor coming up into the unit. Try some of the commercial tank cleaner they have for the grey tank and allow the tank to fill up a few times so it can get a good flush when it drains. Hope this helps!