I always dump mine before leaving the campground and take the time to flush it out. I've never had smells.
Over Memorial Day week-end I dumped Sunday night with the Blue Tote to avoid the dump station with the mass exodus on Monday. We continued using the toilet Sunday night and Monday and figured I'd dump once I got home.
Well, when we got home, we've slept in the camper almost every night since, including showers and using the toilet. I've not had to dump the black tank yet (not full).
Well ... !!!!
Yesterday when I went to use the toilet and pushed the peddle .... OH MY.... what a horrid smell radiated out of that little hole! OH MY!....
So, right then, I went ahead and got the Blue Tote out and dumped (I can dump the tote in my septic tank). So I also flushed the tanks real good again and put a cup of laundry soap down the hole. The next time I used the toilet and pushed that peddle .... no smells. Phew!
I learned my lesson.
There are those who say you can leave "stuff" in your black tank for days on end. Well, maybe you can. But I won't be doing it any more ... ever again! One nose full is enough for me!