Overflow box question

[smitty]

I'm going to drill the back of my 29 gal Bio Cube & put a 1" bulkhead to go to my sump I'm adding. My question is.....Do you think I need an overflow box or is the center chamber just in essence one huge overflow box?

 

[rainydave]

If I remember correctly (it's been a while since I had my 29 BC) you should be okay. The only thing I would be concerned with is the return. If it's too far under water it might create a siphon and pull water into third chamber, and then the middle chamber, until the water drops below the level of the return.