Russian Oleg Kononenko put in the new pump, and the toilet started working normally again.
For two weeks, the three men living aboard the space station had to manually flush the Russian-built toilet with extra water several times a day. It was a time-consuming job and waste of water, not to mention an unpleasant chore.
So everyone - especially in orbit - was thrilled that the new pump seemed to solve the problem.
"Let's start using it," Russian Mission Control told Kononenko. "We'll keep our fingers crossed."
The space station's toilet woes seemed to capture the world's attention. It ended up being the main topic of conversation at NASA news conferences, with fastidious suit-and-tie managers having to describe the ins and outs of using the restroom in weightlessness.
"It's unfortunate we're talking about toilets, but that really is the life, that's the future of human exploration in space," Kirk Shireman, deputy space station program manager, said Tuesday night.
"I don't take it as a really bad thing. It's just something perhaps everyday people can really relate to," he said.
The hatches to the billion-dollar Japanese lab - named Kibo, or hope - were to swing open late Wednesday afternoon, a day after its installation at the space station.
Japanese astronaut Akihiko Hoshide was expected to be the first one inside.
At 37 feet and the size of a bus, Kibo is the largest of the nine rooms now at the space station. It surpasses the two other labs, belonging to NASA and the European Space Agency, by nine feet and more, and it's going to expand.
A large float-in closet for Kibo arrived at the space station in March; it will be installed on the lab later this week. A third section - essentially a porch for experiments - will be launched next spring. That's when full-scale science operations are expected to begin inside Kibo.
Two astronauts will float back outside Thursday to set up Kibo's TV cameras and remove covers on its robot arm.
The space station is now three-quarters complete with a mass of more than 600,000 pounds. NASA expects to wrap up construction in 2010, when the shuttles are retired.