Everyone has there own but typically I use 1 pack of a commercial toilet treatment to get some bacteria in the tank plus they're usually a deodorizer too. To that I add a capful of Calgon plus using the same cap at least a good capful of Dawn dish detergent.
IMO I have found I have better results traveling with stuff in my black tank until I'm ready to dump. I believe the motion of the fluids in the tank help break up the solids plus "scrub" the tank. So when I do decide it's time to dump that's the first thing I do after setting up.
You know, these tanks have square corners and flat bottoms with the valve cut into the bottom without any sump so regardless how long they're flushed or how many times they're filled with water and dumped, $#%* is always going be hung up in the corners.
I'll tell you a story sometime when I see you. You guys coming to any rallies this summer?