do I then set the flow from the return then set the syphon?You need to have a siphon break that keeps water in the overflow. Also, you need to make sure that there's enough flow going through the overflow to keep the air bubbles moving out of the siphon tube into the overflow. Not enough flow causes air to build up inside the tub and once there's a big enough air bubbles the siphon breaks and the sump will pump and drain down the sump and overflow the tank.