Reduced gravity aircraft. AKA the Vomit Comet.

https://en.wikipedia.org/wiki/Reduced-gravity_aircraft

Perhaps buoyancy could be a decent substitute, at least for the solid waste part. I imagine being waist deep and flushing the entire bathroom after each training session. Maybe some kind of spatula/squeegee might assist with separation, coupled with a robotic spatula cleaner and sanitizer. There would be a monitor and cameras so you could calibrate your aim. What an odd workday that would be.