Answer:
Mouth up it gets filled, mouth down it gets empty.
This is a dead giveaway
This is a shape and a symbol that we literally cannot live without. What is it?
What has holes on each side, but can still can hold water?
What 4-letter word can be written forward, backward or upside down, and can still be read from left to right?
What do you purposefully put lots of in and on your body, but run away from when you encounter it outside?