This is what I do using the Geo Method Same mixture as I use in my tank,never ever use any chemicals.
The Geo method claims to use water softener and chlorine bleach; not sure how this is not using chemicals.
Anyway, I never do anything special to my tanks. My RV is 26 years old and we've had it 7 years now. All I do is put one of those blue "poop pellets" in the tank before every trip, and then at the end of every trip I have a small block of wood that holds the toilet flapper open and I let it flush with the water pump on until the black tank is completely full.
To dump, I first dump the black tank, then close the valve and dump the grey tank. That's it. I don't spend time hosing out the black tank or putting special chemicals in it.
We have no smell problems and the fill sensors still work fine.
Personally I think people make too much of a stink (hah) over the waste tanks.
Steve