Human factors like this are some of the toughest aspects of space travel.
Story goes that when they were trying to design a toilet for use in space, they installed the prototype on the "Vomit Comet." Then there was a Second Lieutenant on standby, chugging down a lot of water. And when he finally had to "go", they bundled him into the airplane and took off so he could try out the facilities.
When I worked on Space Station in the '80s, wandered by a desk one day that had a book that undertook to scientifically study the, ummm, "waste ejection process." Had photos of naked men and women standing in front of a gridded background as they urinated. You could see exactly how it came out, and how it traveled in a 1-G environment. Don't recall if there were any photos of similar photography in the Vomit Comet.
As far as, mmm, "solid waste" is that we've got millions of years of evolution depending on gravity to pull the sticky substance away from our bodies. Otherwise, it's hard to achieve "separation." The ultimate solution is "Apollo Bags," dating from that program. This is just like the plastic bags you take along when walking your pooch...but are used to grab the material and pull it away from you. These are apparently still carried as a backup.
The shuttle toilet attempted to provide a more-familiar environment. It used suction past the user's nether regions to attempt to slurp the stuff away. Understand it didn't work real well. The user had to position their "exhaust port" very precisely to have any hope of it working. The seat included handles for the user to position themselves. The ground trainer had a camera in the drain of the loo, and the trainee would get used to the body position required by watching the camera. Story goes they had a camera in the shuttle head as well, this was not the case.
Mike Mullane's excellent book about his time in the Shuttle, "Riding Rockets," mentioned some civilian astronauts (typically those provided from industry, not NASA professionals) who tried to avoid having to "go" in-orbit just because it was such a messy process.
After slurping the stuff down, it was chopped up and dehydrated. Supposedly, two science fiction authors shared the drawings of toilet system, and one said, "Larry, the way I see it, the s*** is SUPPOSED to hit the fan...."
Working on the Space Station in the '80s, we had two Skylab astronauts as consultants... Bill Pogue and Jerry Carr. Pogue wrote a ~26 page book titled "The Astronaut Primer." It was formally published later, but he handed out xeroxed copies. In it, he very bluntly described the physiological issues of living in space. Takes all the romance out of it.....
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Ron Wanttaja