Our toilet is a Thetford Bravura. Low model with full size pan and seat. It is mounted on a black tank inside the cabin that holds about 60 litres.
Below the cabin outside is a flange with a gate valve. The bottom of the flange is a standard thetford cassete adapter.
We use a normal small cassete to simply decant the contents of the black tank away.
Ie a full tank could take 5 cassete's.
I gues you could use a hose to drain the tank. We havent . This method is clean and simple.
The whole system is powered by gravity which i have found available freely everywhere.
Now the yucky bit. After a short drive the content of the tank is pure liquid which makes it easy to dispose.
The tank is vented to outside.
It works fantastically and we could get 20 days ish if we ever filled it it
which we never have.