Answer:
Round as a button, deep as a well. If you want me to talk, you must first pull my tail.
Talks like this, a green wise man does. Guess my clue, you will.
Gets rid of bad ones, short and tall. Tightens when used, one size fits all.
Pregnant every time you see her, yet she never will give birth.
The more you take, the more you leave behind.
Before I grow I'm small. When I'm old I grow tall. When I die I give a mighty fall.