quick overflow question

[rkhlk]

I purchased an overflow with no instructions. I brought it new and it has a small air line coming directly off the top. My question is what is it for and where does it go. Next question is I'm planning on turning everything on later this week to start cycling, but not sure if i need to somehow prime the overflow, or will it pick water when the return pump starts.
Thanks,
rkhlk

 

[reefraff]

You fill the chambers on the tank side and on the back with tank water and use the air hose to suck the air out of the overflow to start it. You really should pick up an Aqualifter pump. You hook it up to the airline and run the outlet into the tank side compartment of the overflow box. It is a self priming pump so it will suck the air out of the overflow and continue sucking out the air bubbles that tend to build up in it while it is running. These pumps are cheap and will prevent the overflow from shutting down when too much air accumulate in it.