I have a Quickie Flush
that I installed on my black tank.
During camping season, after I empty the black tank, I periodically (usually if I'm not going to use the TT for a few weeks or more) rinse it using the Quickie Flush. Regardless, whether I've rinsed or not, my wife always pours an 8oz bottle of Campa-Chem
followed by a gallon of water into the empty black tank via the toilet.
The last campout of the season, I only rinse with the Quickie Flush. No chemicals or water is added to the black tank. When I winterize, I pour about a pint of RV anti-freeze into the empty black tank via the toilet to prevent any small amounts of water remaining in the tank from freezing against the drain valve.