Sounds like your pump has a return line. If your car didn't come with a return line then you have the wrong pump as Carter makes two versions of the Chevy small block pump; one with a return line and one without.
I don't know if it was a California thing or just a Rochester QuadraJet for certain car bodies, but I have seen return lines on full size and Chevelles but none on Camaros or Novas.
Unusual. I used to test those at UL Marine labs when they where still located in Tampa. Has a bras screen inside to absorb any heat of a back fire or other ignition source to prevent a gasoline fire in the bilge.
I saw three holes drilled in the standard fuel pump to vent the diaphragm which I assume you don't have having an external vent line (that would go above the gunnel on an inboard OMS stern drive to rid the bilge of gas fumes).
It won't hurt a thing to leave it as is for a car application. It will prevent igniting your oil pan if you ever drove through a forest fire out west. Otherwise it just drives up the price of the part with the added work done to obtain a UL-Coast Guard rating.