But the belt only moves forward, never backwards, in the video. So I thought the slicer would need to change. A one-way belt also wouldn't have as much proble

But the belt only moves forward, never backwards, in the video. So I thought the slicer would need to change. A one-way belt also wouldn't have as much problems with adhesion, or backlash that you mentioned with a two-way belt. Also, the nozzle moves in the Z direction (not just x). Actually the Z direction is really a little z and a little y.