slight odor from behind thetford aqua magic style II

My odor was from storing the sewage pipe in the basement compartment where the valves are. There was ever so little air spaces that allowed air from the dumping valve area up into the bathroom. Check to see what is located on the topside of that compartment. If you can see your black tank and any hoses or wires going thru the floor consider moving your dumping equipment to a fully sealed compartment. Good Luck.