Old MH I've had since November. Been on a trip for 8 weeks. Dumped twice in last week. 8-10 times overall. Generally on the road with longest stay at 6 days. Only been at park with sewage twice for 2 days each. Have been keeping stuff in tank, than dumping it.
Went on the roof and checked the vent tube but saw nothing weird, but didn't really know what to look for.
Seldom run the fan before or after the odor problem.
Forgot to mention that dump gauge started registering full all the time at about the same time this started. However, since I filled with water yesterday and drained, gauge seems back to normal.