One more hint I should mention.
Through a lot of trial and error, I've learned to make the overflow twice the size of the water inlet. Water coming in is under pressure from the
pump, but the draining water is just gravity fed and cant drain as fast as pressurized water coming from the pump. Making the overflow twice the size keeps it from backing up and spilling out before it can drain, or needing to worry about trying to solve the problem through the timer setting, and/or diverting some of the water flow from the water inlet side. If you use a 1/2 inch water inlet, I would use a 1 inch overflow, or two-1/2 inch overflow fittings.