Fuel tank set up

[A.F.C. 8511]

I received my new 29 gal. Moeller fuel tank for remote installation. The tank has 1 extra port than I can account for.
There is a main fuel line port for the engine. A fuel filler port (the largest port) then there are 2 (TWO) additional smaller ports next to filler. I know one is a deck venting port.
what is the forth port?
picture of tank included.

 

[GA_Boater]

One of the 3/8' fittings to the left of the filler, is a fuel return line for some fuel injected motors. Diesels come to mind and maybe some gassers.

 

[mickyryan]

a return port from fuel pump if applicable? some have a return hose for psi regulation.

 

[A.F.C. 8511]

Thanks guys.
what do I do with it. Plug it, cap it? How? Leave it with that red plug?

 

[GA_Boater]

Close it as it isn't needed. The red cap is only a shipping plug to keep junk out of the tank. Use a plug.

 

[A.F.C. 8511]

Thank u guys.
i appreciate it.