There shouldn't be any smell coming into the coach if the toilet is holding water in the bowl. The black tank if not rinsed with the sprayers (if equipped) after you dump should not smell. But what we do after we dump and turn the sprinkling sprayer that our coach is equipped with. We will dump that water again after the spraying, THEN we will go inside the coach fill up the toilet bowel with water and add some enzyme like Happy Camper so that when the coach is in storage the enzymes will continue to clean the inside of both tanks. You will never have bad smell in your coach again.
But if it still smells, then you could have an obstruction on the pipe between your toilet and the tank, since you mentioned that the tissue is not washing down that four inch pipe.