https://www.nytimes.com/2019/04/30/magazine/how-to-prepare-yourself-for-space.html
How to Prepare Yourself for Space
“You’ve been trying not to pee in your pants your whole life,” says the retired astronaut Scott Kelly, who wore a diaper for liftoff and landing on all four of his space missions. Going into orbit will require you to confront your body in ways you don’t have to on Earth. Get over decades of conditioning by rehearsing basic bodily functions on land: Put on a diaper, lie on the floor with your legs up on the couch, and practice urinating without shame or gravity’s assistance. (Don’t, and you’ll risk damaging your bladder when your body won’t relieve itself in space.)
https://www.thoughtco.com/how-to-use-the-bathroom-in-space-3071528
https://www.space.com/22597-space-poop-astronaut-toilet-explained.html
That's been working for me. Being a couch potato, I don't have to waste time getting up and walking to the bathroom.....