If the the search I did turned up the correct one I like it!! Does it have a darker color mixed into the pretty blue? Did I find the correct one?
Dug through some more of my pics and did some googling and that is the equalizer line for the auto fill.On a new build, that likely is a Venturi line (yes a return, it creates more suction in the skimmer by using the output flow to make a Venturi), needed for the operation of that type of skimmer. It's part of the design of that type of skimmer.