wavebox and overflowbox

If your overflow box is set up properly, the siphon should never break. Do you have a pic of your setup?

With the CPR style boxes, the box on the tank side and the dividing wall in the back side keep the ends of the siphon loop under water at all times. So, even when the tank water level drops, the water stays captured in the box, to keep both ends of the siphon loop submerged.

I have had the best luck with these boxes using an aqualifter pump or a powerhead venturi attached to the airline fitting on the siphon loop. Without this, they tend to gather air in the siphon loop that needs to be manually purged every few days.