Without gravity, using the bathroom is probably a difficult task. It is obvious that a normal toilet could not be used on a space station. According to How Stuff Works, the bathrooms on space stations are built with leg, foot, and lap restraints that hold astronauts in place. One major difference between space and Earth toilets is the use of air as opposed to water. The air is used to draw waste away, where it is then compacted for disposal upon return to Earth.
Even space bathrooms are in need of a plumber sometimes. A Discovery News article discusses that one toilet located at the International Space Station was not functioning properly. To solve the problem, officials had to make room on a separate shuttle launch for a 1/2 foot long pump and its hardware.
Sources: How Stuff Works