Answer:
Men in skirts blow into these.
You fill it and it empties, A metaphor for plenty, Depending on what half you see, It's either full or empty
It is in every mountain, it's not in any hill, it's not in all the world, and yet it's in the mill.
Passed from father to son and shared between brothers, its importance is unquestioned though it is used more by others.
What can be seen but not touched?
When is it bad luck to see a black cat?
Easy
Animal
Difficult
Food
Funny
Kids
Logic
What am I?