I've got a 2012 Sunseeker 2900, it doesn't have the black tank flush feature I've heard so much about, and wanting to learn as much as I can about maintaining my mh I set out on the interwebs to find out how to clean my tanks. I stumbled upon the "geo-method" https://sites.google.com/site/cbruni/
and have been using it for approx two years now. I just dump, add 5 gals of water with soap, water softener, and a little bleach and then drive her home. The only "magic" I can report is that my black tank levels now report properly most of the time, I suspect that's due to the effects of the water softener.
What do you guys do for your tank maintenance?