How do astronauts go to the bathroom?

In microgravity, nothing falls: suction is needed instead. The Station's toilets combine a flexible funnel connected to a hose, individual to each crew member, for a very small-diameter seat sitting above a bag. A fan creates the suction that draws away urine and solid waste, and the air is then filtered before returning to the cabin. The user holds themself in place with foot bars and thigh restraints, without which they would float off the seat. The most recent model was designed to be more compact and better suited to female anatomy.

Nothing is thrown away when everything is expensive to launch. Collected urine undergoes chemical pretreatment, is distilled, and then joins the cabin's humidity condensate in a purification system that produces water meeting consumption standards. This loop reduces by that much the mass of water that needs to be launched from Earth. Solid waste follows a different path: bagged, compressed and stored in a container, it leaves aboard a cargo vehicle that burns up in the atmosphere during reentry.

During a spacewalk, a launch or a return, toilets are not accessible: the crew wears an absorbent undergarment capable of holding several hours' worth of liquid. The earliest missions made do with adhesive bags and tubes, a less-than-glorious memory that accounts of Apollo have not spared. The lunar programs now in preparation are still seeking a more dignified solution for long excursions.