In warm weather if you are on site and don't dump but once a week or less the chemicals that fight odor and help with breakdown make good sense. We usually use liquid but have on board the packs and use them.
Sitting still for a whil while warm will make it stink pretty bad other wise sometimes.
When we ump after sitting for a while and some other times we put some calgon and some soap liquid dish soap too.
Ten when we fill to flush it stirs things up and the pressure flushing gets it all out. Maybe over kill but so far no black tank problems.
We of course pressure flush the gray tank last and the shower soaps, laundry detergent, softener and such really cleans the hose out. Only once or twice have we sensed the need to refill the black tank with the flush system and flush again and a good idea when going into storage.