The bowl has come loose from the base of the toilet in my motorhome. The bowl is porcelain and the base (with the flush valve) is plastic. Looks like I will have to remove the toilet and turn it over ...
Do a twist to get it off the flange if you cannot get the nut off the screws. I didn't and broke my flange. Also, don't over tighten to the flange. I did and broke it. Good news is the local hardware store flanges worked fine. Good luck.