Well I guess since you can't just "go outside" it is a bit of a problem. 
Link…
Link…
National toilets?The International Space Station, once a place where astronauts would share food and facilities, is said to be embroiled in a Cold War-like stand-off.
A Russian cosmonaut has complained he is no longer allowed to use a US toilet as well as a US exercise bike.
Gennady Padalka, 50, told Russia's Novaya Gazeta newspaper the lack of sharing was lowering the crew's morale.
"They also recommend us to only use national toilets," the newspaper quoted him as saying.