Answer:
What has 3 feet but cannot walk?
Until I am measured I am not known, Yet how you miss me when I have flown.
The more holes you cover the lower it goes.
Always old, sometimes new. Never sad, sometimes blue. Never empty, sometimes full. Never pushes, always pulls.
What is the thing which, once poured out, cannot be gathered again?
You use it between your head and your toes, the more it works the thinner it grows.