The hands move in a spiral and the hips drive the movement.
personally, i think folks focus too much on the hands. don't pay much attention to my hands or uke's hands for that matter. only interested in uke's shoulders and spine. the up part, i would try to slap uke's head with his/her own shoulder. the down part, i would try to hit uke's with his/her own elbow. essentially, taking half of uke's body up and the other half down. that's just a simplified explanation. there is more to it within your own body, of course.