Well...don't feel like the lone ranger, lenOrge
Been using 'Campa-Chem' dry powder (Thetford) because it's advertized as biodegradable. Like others, I also dump in cup or so of inexpensive dry laundry detergent into BOTH tanks when we hit the road, to take advantage of the splishing 'n spashing action.
Was amazed to learn that good ole Dawn may do the trick all by itself ??? Hmmm.