Got 2 of those sitting in my junk box at home Greg. They do not work at all! They stop the syphon for a second, then they "burp" and the flap opens a little and releases water.. this continues until your tank is done back syphoning. So it doesn't all rush back into your sump as once.. but it still happens very quickly, within a couple minutes.
Normally people rely on their sump only being 1/2 full and being able to handle the back syphon without overflowing.
Normally people rely on their sump only being 1/2 full and being able to handle the back syphon without overflowing.