I have used Odorlos
for years. No chemical smell and no tank smell, although we don't use the black tank heavily nor let it sit and fester for days.
A tt tank is a holding tank, not a septic tank. Use whatever bowl cleaner you would use at home. We use a locally sourced "Natura" product that also doesn't smell as I can't stand the strong odor of common bowl cleaners in a confined space. If you're still concerned, clean the toilet just before dumping and the bowl cleaner is gone.