Hi reefcrazy
What do you mean the overflow doesn't work ?
I mean I know it doesn't work - but how so ?
Did you remove air and prime it as coralfishg2 has described above ?
Have you tried raising or lowering the inner slotted box.
Does the overflow's outer box have a raised bulkhead fitting, like a standpipe that comes up into the box ? Or does it have a chamber or wall that maintains constant water level in this outer box ?
The outer box must have one of these two methods of keeping the water level somewhat constant in the outer box.
I've seen some good designs and some poor designs, can you describe your overflow in greater detail or even better post a pic ??