As has been said, if your black tank system is fully sealed from the tank up to the vent, you should not be getting any long term smells. Yes, if you flush and have vents running you could draw some of that odor up but it should dissipate rather quickly.
Does your toilet hold water between flushes? If not...fix because that is a probable source of odors.
Do you have any leaking below the base of the toilet? If so, another possible source.
Have you checked your basement to make sure there isn't a leak below the toilet? If so, your basement should be just as bad as the coach.
Check the roof top vent for debris and blockage.
Consider a 360 Siphon vent cover
. Works great under nearly any wind condition. Along those lines, does the leak come and go with windows open? Occasionally a light wind from the wrong direction can cause odors to drift down the side of the coach and back into it through a window.
Have you checked all GREY water traps to make sure they aren't dry? As an example, if you have W/D hook ups but don't use them they can dry out and allow grey tanks smells to enter the coach. Some think the grey tank is worse than black. Pour water into any suspected traps (most likely W/D) and see if that fixes the problem.
Don, Sandee & GSD Zeus. Gardian Wings earned are GSDs Gunny (7/11/15) & Thor (5/5/15)
2006 DSDP 4320, Spartan MM IFS, 2013 CR-V, Blue Ox Avail, SMI AF1, Samsung 197R Refer.