Here's a description of my set up. I have a 5 gal glass carboy (water jug) with a rubber stopper in it. Two pieces of rigid air tube pass through the stopper (just drill the holes with a drill), one to the bottom of the jug and the other just through the cork to let air in. Siphon the water from the bottom of the jug with a flexable air hose. To keep all the water from going in, I have a length of PVC (1" x 2ft) which has a stopper in one end and the other end just below the water level in my return. Connect this to the short tube with some air hose. Now, when the water level is above the bottom of the PVC, no air can get into the jug so the siphon stops. As soon as air gets in the PVC, the syphon resumes.
Works like a charm with no valves, switches or electronics.