Overflow box not siphoning

[Johnny Reefer]

IMHO I think you should go back to the way you had it 3 months ago until you can invest in and set up a drilled tank. Don't even bother with a siphon overflow.
I learned my lesson with siphon overflow boxes 9 months ago.
Didn't have a flood but I could see one comin'. Not worth the risk.
Got a drilled tank now and it is waaaaaaaaayyyyyy better.
Maybe not the answer your lookin' for, but that's my humble opinion on it.

Cheers,