Hey so Chris Hadfield wrote us an article (!) involving pooping and peeing (!!!!!!!).
#5. Going to the Bathroom in Space Is Awesome
For the solid waste, air sucks it into storage, where it’s exposed to the vacuum of space, which kills off any bacteria and neutralizes the smell. We have to brace ourselves in order to keep the digested remnants of our freeze-dried ice cream from floating off into the station, but other than a bit of an upward draft, it’s rather comfortable. The waste is packed onto returning supply ships, which burn up when re-entering the Earth’s atmosphere (so if you saw a shooting star in early 2013, you might have had me to thank, although I wouldn’t recommend wishing upon it).
For urine, men use a funnel and women use a cup. These attach to a tube that sucks the urine into storage, where it’s later converted into drinking water. It’s expensive and impractical to bring water up to the station, so every drop of refinable liquid counts. And you can pee upside down, which I did, just for fun. Wouldn’t you?