Overflow box not siphoning

[wetcoast]

So after my boss sent me home early today to take care of the mess I was about to deal with - I came in and noticed why my fish were gasping for air this morning, I only had one powerhead going all night due to my mucking around to see if the powerheads were broken (to answer the above question). The airstone and extra powerheads I threw in before going to work helped alot, all livestock was alive.

I decided to give it a whirl again today and everything worked as planned without issues! I just don't understand what the heck is going on here. Mind you - I don't trust it. Looking for a 65gallon tank to drill and then will sell this one.

The saga continues.