The Russian-made toilet, which cost $19m, failed last week. A broken fan and pump meant that the facility could not handle liquid waste and astronauts were forced to use a much smaller system in the station's emergency capsule.
The device has now been repaired using a part brought up on the Space Shuttle Discovery.
"It does appear that the service-module toilet is back in business," said Nasa mission control broadcaster Rob Navias. "Three separate tests indicate good air flow."
If the repairs had failed Nasa did have a backup plan. The Shuttle also carried a supply of plastic bags treated with adhesives and antibacterial substances.
Space Station fixes number one priority
By Iain Thomson on Jun 6, 2008 10:34AM