3rd plastic line in tunnel, 1975 2.0, what is it? Options

[jhynesrockmtn]

I have a friend who is restoring a 1975 2 liter car, original injection. The car needed quite a bit of metal work done and he has finished that and had it painted. He took the engine out a few years back. My experience is with the earlier cars.

We pulled the fuel tank on Saturday and he is ordering parts including new metal fuel lines. When I was looking in the engine compartment I noticed another plastic line exiting the tunnel near the plastic fuel lines but it was clear or close to that. I can't find it on the parts diagrams I've looked at. What is this line and where would we order a replacement? It is brittle after almost 50 years and he is wanting to do this right.