Dan, If you're talking a 'general' cleaning, I've used 1/2 cup of Dawn dish washing liquid with the same amount of bleach and Calgon water softener added to 10-15 gallons of water in the tank. Drive to your next CG and when the tank is 3/4 full, dump the tank. I do this maybe every 4 to 5 dumps. We do not use deodorizers with this method.
Now if you're talking the dreaded 'Pyramid', one of those 'flush wands' hooked up to a water hose would help break the solids up if the toilet is located directly over the tank. If not, I've read that some products with enzymes will hasten the break down of waste after a long soak. Good luck, Bob