I prefer the slosh it around method to cleaning the black tank. Our MH has a tank rinser built in that definitely helps. After dumping the tanks at the campground, I put in a few gallons of water and a bottle of tank deodorizer in for the trip home. When I get home, I fill up the black tank with the tank rinser and dump it. After a few hours on the road, most contents of the black tank are broken down and come right out.
After a few fill ups and rinses, the RV Flush is usually pretty clear. I don't use the RV Flush to rinse the tank for the same reason you found. I could tell during the first time I used it that it was not putting much water back in the black tank. I bought it for our HTT that does not have a built in tank rinser.
It is a great video.
-Michael
