Even when astronaut guest blogger Leroy Chiao isn't asked, he knows people are dying to know: What's the deal with relieving yourself when there's no gravity to contain the mess? How does it actually work?
In the early days, there were no restroom facilities onboard spacecraft. The first flights were only supposed to last minutes, so it was thought that there was no need. The story of Allen Shepard having to relieve himself in his suit became common knowledge, after the event was dramatized in the movie, "The Right Stuff." Later spacecraft, including the Apollo spacecraft, also had no toilet facilities. The crews of these vehicles used modified piddle packs (used by the military), which utilized a condom, attached to a hose and bag, for collecting urine. What about women? Back in those days, there weren't any in the space programs (except for Valentina Tereshkova, who probably used a diaper), so it wasn't an issue.
For collection of number two, modified sealable bags were used. There was no privacy aboard the Gemini and Apollo capsules, so imagine doing all of this in close quarters with your buddies! To make matters worse, these bags were (are) clear. They are still carried aboard US spacecraft, for use in the event of irreparable toilet failure.
Fortunately, things got a lot more civilized in the Shuttle program. As I mentioned before, the Shuttle is a business class affair. It contains a relatively large toilet area, which features a privacy screen.
The Soyuz capsule also has a toilet in the upper living module. When someone has to use it for number two, the other two crewmembers can retreat to the descent module, to give the third guy a little privacy. Usually, that toilet is not used for that purpose, though. Crews go through a preflight enema, which usually is enough to clean you out for the two days of flight it takes for the Soyuz to phase, rendezvous and dock with a space station.
The toilet aboard the International Space Station (ISS) is the same as the one that flew on the MIR station. This is also a civilized affair, in a relatively large area, with a privacy screen.
So, how do these toilets work? They all basically work the same way. In the absence of gravity to help you, airflow is used to try to collect everything and point it in the proper direction. To urinate, it is pretty simple. Use the long hose, which has a funnel attached to the end. Turn on the system, and make sure there is good airflow before relieving yourself. Make sure not to actually contact the funnel with your valuable parts; it's a disgusting thought first of all, and second of all, you wouldn't be able to shut the system down before you really regretted getting the life sucked out of you, so to speak! By the way, this system works for women too. The suction is adequate to make sure that the liquids go to the right place.
For number two, the seat lifts up, revealing a small hole. You've really got to get to know yourself, and get good at lining things up for this operation! The system again uses airflow to collect and hold things down where they're supposed to go. After you're finished, the bag is tied off and pushed down into the replaceable silver can.
Accidents do happen, and by international agreement, you clean up your own mess!
Is it worth it? One of my crewmates on Space Shuttle once told me that he wished that we could land every morning, so that he could take care of business there, before launching back into orbit. Yeah, it's not pleasant, but you get used to the hassle of doing these hygiene tasks. It's not so bad.