I am still wayne_tw wrote:
Water, water, and lots of water. Did I say add lots of water? Fill the tank with water. Let it sit for several days. Driver around and let it slosh. Then drain and repeat. What has happened is there is significant residue left in the tank. Check to see that there is water in the toilet bowl. If not, fumes is coming from there. Some RVs have a one way vent to the black tank somewhere under a cabinet. It could be allowing fumes into the RV.
Add a bag of ice cubes also .. at least that is what we had to do, then drive around ...
And the tank should empty right away ..