I've gotten to the point, after two decades of RVing, that I use the toilet, occasionally watch the gauges, and see when it's getting close to full. I then close the grey valve and wait. The next day I dump the black, and chase it with a partial load of grey.
No Rid-X,Geo method,expensive blue stuff from the camping store, Ice, black magic, or ancient Chinese secrets. If the RV has been parked while snowbirding, and hasn't moved an inch,after a few months it will develop the dreaded "Mount Poosovious". I then take a wand that came with the rig, hook the hose to it, and give the tank a blast. The wand was free, it has a cool brass spinning head on the bottom, and for the once a year I need it, it works great. IF, and only if, it's a hot summer and things are getting funky in the black tank, it gets a shot of straight, dollar store bleach, every so often.
That's my story. No drama, no need for any fancy methods, techniques, or expensive chemicals. Poop, store, drain, repeat.