Mostly covers for different hoses and valves for scientific instruments used underwater. For the seals I mostly use O-rings.
I myself have made a couple of very simple watertight (non essential) prints for scubadiving. They are holding up really well!
The guys from Prusa Research have a lenghty blog post about watertight 3d-prints: https://blog.prusa3d.com/watertight-3d-printing-part-2_53638/ This might be a good source for tipps and tricks!
I am currently playing “It takes two” together with my wife. It looks cute, has a story that is funny and really sad at the same time and the mechanics of the game change frequently. The occasional (optional) Minigames are really fun too!
I turned on the “wrong water” in the shower. (?)