How do I move all items in a connect list to another list?

How do I move all items in a connect list to another list?

I have two connected lists (sortable1 and sortable2) ... and I have two separate buttons.

Button 1 to move (append) all items from sortable1 to sortable2
Button 2 to move (append) all items from sortable2 to sortable1

How?

TIA,

Bob