1 Terry: You can’t bring Steve back through sewer pipes in pieces and expect to reassemble him!
2 Jane Goodall: Who said anything about reassembling? Anyway, that’s how transporter technology works in Star Trek.
3 Terry: That analogy is no good! They don’t use sewer pipes!
4 Terry: In fact... did they even have toilets on board the Enterprise??

You could be forgiven for thinking that none of the starships shown in any Star Trek series or movie ever had toilets, because we never see any evidence of dedicated bathrooms. There are, according to the nerd hive-mind of Memory Alpha, exactly two on-screen shots of toilets in Star Trek:

• In the film Star Trek V: The Final Frontier, when Kirk and others are confined in the ship's brig, Kirk presses a button which extends a toilet from the wall - so he can sit on it. Amusingly, there is a legible label on the toilet saying "Do not use while in spacedock", which implies that the waste is simply ejected into space rather than being processed and recycled in a way that would actually make sense - no doubt a deliberate joke alluding to similar restrictions on toilets on board trains.
• In the Next Generation episode "Q Who", in which the Enteprise-D first encounters the Borg, there is an external shot of the ship taking damage from a hit and some debris drifting off into space, which includes what is apparently a toilet.

But we never see people go into a bathroom or shots inside such a facility. It would be cool for a scene to take place between some redshirts who are chatting while relieving themselves, but it never seems to happen. Maybe that's why they're so keen to die.