Answer:
I go around in circles, but always straight ahead. Never complain, no matter where I am led.
Gets rid of bad ones, short and tall. Tightens when used, one size fits all.
What is full of holes, but can still hold a lot of water?
What an fill a room but takes up no space?
At night I come without being fetched. By day I am lost without being stolen.
If I say "everything I tell you is a lie", am I telling you the truth or a lie?