Overflow question

[Anonymous]

I have a hob overflow box I'd like to use on my 35g. The external part has a divider which reaches about 2/3 to the top. The left side has a bulkhead attachment for the drain which is 1 1/14". The right side has a 1/2" hole in the bottom. Could any of you tell me what the right hole is for and the purpose of the divider? Thanks all.

 

[Ben1]

The divider is there so the U tube is always under the water level and doesnt lose syphon in a power outage, but I dont know why there is a 1/2" hole.