[DutchmenSport]

How close to the ceiling air vent, fan and the vent for the black tank from each other on the roof? I have heard stories in the past where black tank odor was inside the camper. It turned out when the wind blew the right direction, it would blow the black tank oders from the black tank vent on the roof directly into the ceiling fan on the roof and into the bathroom, causing .... bad smells inside.

Check it out. It might be just that simple. (or maybe not!)

Also,
If the bathroom ceiling exhaust vent fan is running and you push the pedal of the toilet, the slide valve in the toilet opens. The ceiling vent fan will pull air upward through the toilet. That air is sucked INTO the black tank from that same black tank vent, up the toilet and into the bathroom with a lingering aroma of yesterdays steak dinner!

Make sure when you "flush" the ceiling fan in the bathroom is off. Same if you have a ceiling fan, exhaust, vent in the kitchen. Turn it off when you flush. See if that makes a difference.