oder problem

I have an Itasca 36F that has 2 bath rooms. Love the floor plan but I have a problem. The small mid coach bath room has a terrible odor as does the compartment below where the black tank pump is located. I have used plenty of the black tank deodorant pills, lots of water, flush it often, checked all fittings and clamps and still have terrible smell. Could this be a vent problem? Has anyone else had this problem?