I use a combination of the small bottles and the water softener/Dawn detergent mix. When I dump, I flush the black tank thoroughly using the built in flush connection. Then, once empty, I mix two gallons of water softener/Dawn with hot water and put that in the toilet and flush. I also put one small bottle of the toilet chem in and let it do its thing. I use Calgon lavender-scented water softener....makes the coach smell nice. No black tank sulfur smell, (sensors don't work, but they never have), and everything that comes out when I dump the next time is liquid. Maybe a bit more work up front, but I plan to keep my RV a long time and I feel like a little bit of work along the way is worth it.
