If you do wanna go ghetto, why not drill a hole at the top of the pipe, stick in a piece of airline tubing, seal around it with silicone, and feed it over and into the tank:
Water will exit from it into the tank when in normal operation. When the return pump stops, air will get sucked into the airline tubing, and break the siphon.
Only problem is that it may get clogged if there is debris being shot up by the return pump, and it may clog after a while... Or you could use some sort of tubing with a wider diameter.