Golly, I think chemicals are optional in RV tanks. Most are nice deodorants and little else in my view. I tried one product that turned the dirty water a nice blue, but nothing else that I could see.
After emptying and rinsing your tank, add two or three gallons of water to it so it stays wet. You don't want solids to harden up on you in there. I leave mine wet all summer. And RV style single ply paper seems to break down faster than the thick, comfy stuff. I drain my tank for winter.
My system combines black and gray water to a certain extent just to add capacity as gray water accumulates faster than black water. I feel good rinsing is important. I rinse until I have clear water coming out.
I just haven't noticed any advantage to RV tank additives.