I think I figured this out. After dumping our tanks, I noticed a really bad smell when I got home. Well it's really simple when I think about it and maybe I could be wrong, but here goes. It seems to me that simply draining and flushing the black tank stirs up the solids and yes the odor will migrate up through the toilet, there's no S-trap to trap the gas. Especially when you add the enzyme and more water through the toilet. What I did yesterday was did my normal black then grey tank drain, added about 6 gallons of fresh water with dawn soap to black tank (again there I go opening the black tank seal by flushing the toilet so yucky smell hello!), drove down the road a bit and drained again, then flush through rear flush connection, got home and added the enzyme with 3-4 gallons of water AND this may be the key, added maybe 1/2 cup water to the toilet, this will simulate an S-trap on the toilet itself. No more sewer odor!!! Yeah!!!!! I foregot to mention, this is my first TT so I'm alittle slow at these things!!
I hope this helps anyone whom maybe having similar concerns. Whew....I think I need to use the RR now! LOL