Valve Assembly for dual fuel tank

[chevyhubcap]

I'm working on a 78 shortbed with dual fuel tanks. A previous owner apparently replaced the valve assembly at some point in the past with an incorrect valve as the vent lines were blocked off. I purchased a new valve from a GM dealer but now have a question.

 

The new valve is set up for 2 incoming lines from both the right and left fuel tanks one is a 5/16 the other 3/8". No problem there. It also has two out going one 5/16" and one 3/8" as well as what appears to be some sort of overflow outlet with a short piece of tubing attached to it.

 

I know the 3/8" outlet line goes to the fuel pump, but what about the 5/16" outlet? Where / what does it hook to?

 

Help appreciated

 

chevyhubcap