I'm in the "Lots of Water" camp also. I flush my tanks all the time, no problems with smells. I will also add a bit of water and a bit of Dawn Dishwashing liquid to the tanks and hit the road (usually on the return home). The soap sloshing will clean it pretty good. Once home, I dump out again. For years, I'd just catch it in a bucket, only a couple buckets full, and then dump that down the toilet at home. Worked just fine. Then I created a way to dump into my septic tank and been doing that ever since.
I also backflush my grey tank into my black tank (every time I dump) and this also help pull out a LOT more "stuff" from the black tank. With the backflushing, and the black-tank-flusher attached to a hose, I never use chemicals, only Dawn on the return trip home.
Water, Water, Water! That's all you really need to keep smells away.