https://www.wired.com/story/how-to-go-to-the-bathroom-in-space/

Former shuttle astronaut Mike Massimino will never forget the time he had to practice pooping for NASA. Before heading to space for the first time, Massimino found himself in a mockup of the space shuttle pretending to use a toilet with a camera inside the bowl. Massimino tracked his own butt using a live feed of the toilet bowl camera, to ensure he was in the proper position. It was harder than it looked.

“The key is alignment,” Massimino says. “Pooping in space was really involved and you really didn’t want to mess this up.”