A toilet is used to stash items to avoid getting caught. It is possible to flush it, but there is a chance of it being flooded. The toilet is more likely to be flooded if there's too many items or dirt/sand in it.

A flooded toilet is clogged. To unclog it, use a plunger on it, or just have a guard do it if you don't have one. If a guard finds contraband in your toilet, you'll be sent to solitary with this note:



You won't be sent to solitary if the flooded toilet is outside your cell. When a guard sees a flooded toilet, the heat gain sound effect plays and the guard says "The heck?" and unclogs the toilet. If you place the dirt by the toilet instead of inside of it, the same thing happens, except the Dirt Found Warden's Quote:

If you are shakedowned, transfer your contraband from your desk to your toilet to avoid solitary!