I don't. I find the cleanest one, wipe it down with TP, and then drop anchor. I avoid port-o-potties and outhouses, however. I'll unload before I leave if I know I'm going somewhere where there won't be plumbing.
You should add an option for the seat covers that many places use. It's handy dandy toilet-seat shaped piece of paper so you don't have to fiddle with balancing the toilet paper strips on the curved seat.