SpaceX is having to fix its leaking toilets ahead of its planned launch at the weekend.
They want to ensure the toilet does not leak after problems were reported.
Works are also underway on another spacecraft which has been parked at the International Space Station since April.
SpaceX’s Vice President William Gerstenmaier said the problems occurred when a tube became unglued during SpaceX’s first private flight last month.
This resulted in urine spilling onto the fans and beneath the capsule’s floor.
He said: “We’ve fixed this problem in the tank by essentially making it an all-welded structure, with no longer a joint in there that can come unglued and become disconnected.”
Meanwhile, Nasa’s commercial crew programme manager Steve Sitch said there was still “a little bit of work to do with SpaceX leading forward to flight” at a news conference on Monday night.
Mr Gersteinmaier confirmed SpaceX is conducting tests to ensure the spilled liquid did not damage the orbiting capsule over the past six months.
Any structural damage to the capsule could endanger the lives of astronauts on their flight back to Earth next month.
The tests will be finished by later in the week. Engineers will present their findings on the capsule’s toilet system and other aspects of the mission to management during a review on Friday.
Mr Sitch continued: “What we’re looking for is tiny clues or tiny, tiny imperfections, that somebody might look at a plot and wonder: why did that temperature go up here, or this pressure change here.
“So you really just try to dig into all those sorts of things and try to understand those, and then improve things and fly safely.”
The launch, from Cape Canaveral on Sunday, will mark SpaceX’s fourth launch of Nasa astronauts and its fifth passenger flight overall.