Manual says as does reasoning, that after flushing black tank to put back in about five gallons of water. That much water sloshing around going down the road is bound to loosen anything in it up. I doubt I let five gallons back into the tank put perhaps three gallons bag and two gallons or so gallons of water and the bag of ice going down the road sure will. The soap,water softener, and commercial black tank chemicals work. It's been a while since I read of pryamids in black tanks here. They always seem to be from those without flush systems or they use the facilities, at campgrounds and are in a hurry or don't want to hold people behind them up or just don't think and drain the black tank or most of it, perhaps but certainly not all of it and voila they all of a sudden realize they have a problem, some 100 degree day in mid July at a campground when the RV really stinks, or they turn a roof fan on, anywhere in the RV and stink the place up. Our RVs are particularly tight, and if the vent pipe to the black tank is the only place air can get in you stinka the place up.