One of the most popular questions former International Space Station crew member Tim Peake gets asked is, "How do you go to the bathroom in space?" The short answer is "carefully." And it's a good idea to practice your form [source: Peake].
Because there's no gravity, extraterrestrial plumbing relies on vacuum suction. Nobody wants free-floating human waste, so the two toilets onboard the ISS are designed to actively suck down urine and feces. (Think high-tech vacuum cleaner.)
These commodes have long hoses affixed next to the seats where astronauts go No. 1. (Two interchangeable funnels are available for the crew members to use — one for males, the other for females.) After selecting the appropriate funnel, they attach it to the hose and then flip a switch to activate an internal fan that pulls their urine into a storage container [source: Izadi].
So what's the deal with pooping on these potties? It comes down to the same basic idea. Space travelers have to go into a tiny vacuum opening that's just 4 inches (10.16 centimeters) across. Most of us in the developed world have gotten used to toilet bowls that are at least three times wider. Aiming poo into such a narrow hole takes serious skill [source: Rowan].
For a time, two replicas of these old ISS toilets were on-site at the Johnson Space Center. The first was called the positional trainer. It wasn't functional, but it did have the exact dimensions of the genuine ISS potty. Inside the bowl, there was a camera that hooked up to a TV monitor facing the seat. Astronauts used that to check their aim while ... ahem, "aligning" themselves. Once a trainee got the hang of it, he or she would graduate onto the newer ISS replica toilet, which actually flushes [source: Rowan].
While these particular space johns are no longer in service — the newer toilets are part of wastewater system that recycles astronaut urine back into drinkable water — they still rely on suctions and vacuum, so astronauts still have to practice up on going potty.