Answer:
Put into a pit, locked beneath a grate, guarded through the night, yet it still goes out.
No matter how little or how much you use me, you change me every month.
It's anything but amusing when this body part gets hit.
Jack and Jill when up the hill jack fell down
To cross the water I'm the way, for water I'm above. I touch it not and, truth to say, I neither swim nor move.
Pirates put their booty in it.