Black Tank Ordor Solution

The black tank odor should not be coming back thru faulty Studer-type vents in your sink plumbing since those drain to the gray tanks. Likewise losing water from any p-traps will not affect your black tank (although gray tanks can also have a very nasty smell). I suspect you either don't have a good seal in the toilet sliding valve, or your toilet is not properly seated to the floor and the downpipe, or you're getting sewer gasses out of your rooftop black tank vent that is being drawn into the rig thru other roof vents. I've run into that at times with other rigs we've owned, usually depending upon which way the wind is blowing. One other possibility, but highly unlikely, is the toilet down pipe has become detached from the top of the black tank, but then I would suspect you'd see some evidence of leakage under the RV.