How does the bathroom work on the ISS?

On Earth, gravity does the work of a toilet. In weightlessness, a fan does it instead: it draws air through the toilet and carries everything that enters along with it. The crew secures themselves with foot straps and handles so the body doesn't float away. Filters clean the suctioned air before it returns to the cabin; without this circuit, odors would be the biggest problem on board. Mastering it reliably takes practice: newcomers train on the ground with mock-ups that have a camera in the bowl, to find the right position.

For urine there is a funnel at the end of a hose, which women and men use with different adapters; it can be used either sitting or standing. Solids drop through a conspicuously small opening in the seat into a bag placed inside a container. When the container is full, it is sealed and replaced. The narrow opening isn't about saving materials but about physics: the smaller the cross-section, the greater the suction. Malfunctions are uncomfortable but anticipated: spare parts and emergency bags are available.

Urine isn't simply waste. It's routed to the water recycling system, where it's distilled and processed together with condensation water from the cabin air to produce drinking water: a loop that saves costly resupply flights and will matter even more for future lunar missions. Solid waste containers, on the other hand, are collected and disposed of via an uncrewed cargo craft that burns up on reentry into the atmosphere. The newest models are more compact and quieter, so they also fit in cramped spacecraft.