I once opened a portapotty at a local sporting event to see a literal mountain of shit rising from the cistern/tank it all goes into that came to a peak about 2 or 3 inches above the seat. I am, to this day, confounded as to how and more importantly why the last few poopers actually managed to get the shit that high without sitting directly on the mound.
I imagine them like those climbers/parkours that go up the walls by pushing 🫷🫸 their hands on both side walls to go up. When they reached the top of the porta potty they started their shitting procedure.