The toilet paper and waste should break up on its own, provided you put enough water in the tank and it has time to break up. Conventional wisdom is any septic-safe tissue is OK to use, you don't have to buy the overpriced "RV" toilet paper. Angel Soft is pretty popular. But, "late deposits" will be a little reluctant sometimes, especially if you're heavy on the paperwork.
As for chemicals, all I put in the tank is a cup of powdered Calgon water softener, mixed in a bucket of water, after I've dumped and flushed the tank. There is the "Geo Method", which uses dish soap, in addition to the Calgon, but the Calgon alone works for me. If you can't find the powdered Calgon, the liquid type is OK, too.