Hello. I have a vanishing edge pool with two pumps, one for the pool and one for the vanishing edge basin. I keep them running 24/7 all summer. However, whenever I turn off the basin pump, water pours out of the "built in" overflow pipe included in the autofill. I am using a basic Pentair T40 autofill. When I open the autofill lid (while the pump is off), the water level is always above the overflow pipe, which forces it to empty out the pipe. I do not have this problem when the pump is on, only when I turn it off. The overflow pipe functions as it's suppose to when in operation (heavy rain, etc.) Does anyone have an idea why this would happen? Is my water level too high in the basin? (it's about 12"-18" from the top and is 3 ft. deep). Do I need to adjust the autofill mechanism somehow? The pool and vanishing edge runs perfectly other wise. Thank you in advance.