How to dump the water on the spinning mop

Relying on centrifugal force, the water absorbed on the mop is denser than the mop cloth strips, and will be preferentially thrown outward by centrifugal force when rotating centrifugally, thus detaching from the mop.

You can do a test: find a piece of dry towel can float in the water, wet, and then hand wringing (do not make too much force, so that the towel will not ooze out of the water but still wet to the touch on the line), and then in the right place vigorously fling this towel, you will find that around the splash of water beads.

Of course this has something to do with how much the mop is pulling on the cloth. If the mop doesn't have traction on the cloth, then the water droplets won't have a large enough acceleration relative to the cloth to fly out. It's like flinging a wet towel without tugging on it, so the water doesn't fly out but the towel flies out with the water.