I appreciate you guys carrying on the discussion to help educate me about cassette type toilets
However, this is just entirely my opinion, that there is no greater, more convenient option than to have a large black and grey water tank with either the regular hose for dumping and better still a nice flexible hose and macerator pump.
Some areas I have camped are so beautiful almost pristine that even the most discreet dumping of grey water into a drain would bother most peoples conscience and not going to the septic dump station. Think about tenters... they don't want to smell stinky grey water emanating from a drain while doing their dishes at the water spigot.
I think a lot about other people too quite a bit.