Even if the society in Star Trek has evolved into a cashless state, that still leaves the matter of stools and other bodily excretions (not sweat or blood) to deal with.
Where does that all faecal matter and urine go?
Having not seen any depiction of toilets or water closets in any of the films or TV series, there has to be a way to deal with this basic bodily function. They're not the Brady Bunch after all.
They eat fine and drink plenty of tea from the replicators. And that Neelix fellow on Voyagar sure cooks up exotic meals. All that has to be handled in some hygienic manner. It's not like they stand around the transport room and have their bowels expunged into space. Do they?