Folks: read Astronaut Mike Mullane "Riding rockets" for an (hilarious) account about how they solved the teething issue of testing a Skylab / Shuttle 0-G toilet on earth solid ground and 1-G.
You guess, KC-135 Vomit comet, and zero-G parabolas (as was done in pre-CGI days for space movies, hint, Apollo 13).
...but there is a major issue there. Zero-G parabolas only last 30 seconds... so the (very) brave volunteer needs to take a dump during that short span of time.
So they kept the Vomit Comet on alert at an airfield like a Cold War nuclear bomber, waiting for the volunter bowel movement (no idea if they gave him laxatives just to help). As soon as the guy come screaming "this is the right moment !" they took off in a hurry, climbed, and made the parabola and, well, the rest, as they say, is history.
That was for Skylab of course, which only had male astronauts. For the Shuttle they had an even more untractable issue to solve.
How do you make a women pee in Zero-G (condoms with tubes won't work there !) and also - how do you test that onboard the Vomit Comet ? Well, some NASA nurses based at Houston Ellington field had some... interesting memories to tell, about this.
When Mullane heard their tales, he laughed so hard like an idiot, coffee sprouted out of his nose...
