I have a 65 caravel
that I played the toilet dance to; there may be a rubber or wax or duct seal gasket. if it's been on there along time, it may hold on to it like glue! just keep pulling and rocking and if you break it, a new one is a great investment. I was lucky! to reseal the joint between the trailer and the toilet, I had to use 2 gaskets; the new rubber one didn't quite seal, so I needed to remove the toilet AGAIN and add a little plumbers putty to stop the drips!!