I once had a player that wanted a Decanter of Endless Water just to waterboard people ๐ณ
Except if the guard manages to rip a hole in the bag from the inside, they can destroy the bag and everything inside it will get scattered across the Astral Plane. Pretty bad for the guard, but better than a slow death being suffocated. Plus you don't need to eat or breathe on the Astral, so they could live there indefinitely.