International Space Station toilet breaks down

"Earlier today, the US Waste and Hygiene Compartment was shut down after a malfunction," said NASA in a statement. "About six liters of pre-treat flush water is believed to have flowed into the pump separator and into other areas it should not be."

Mission Control told the crew to hang an "out of service" sign until the toilet can be fixed. The crew of the shuttle Endeavour is confined to using the craft's loo. ISS residents are using a back-up toilet in the Russian part of the station. If repairs fail, Apollo-era urine collection bags are on hand, Nasa said.

The toilet repair work fell to Belgian Frank De Winne and American Michael Barratt, who had to don goggles, gloves and masks. They ripped apart the compartment, working well into the evening. Mission Control finally instructed them to call it a day and resume the effort Monday morning.

Flight director Brian Smith declined to speculate whether overuse caused the toilet trouble.

"We don't yet know the extent of the problem," Smith told reporters. "It may turn out to be of no consequence at all. It could turn out to be significant. It's too early to tell right now."