Fuel Leaking Problem

Hi there . New to forum and hope my question is appropriate for this feed. I too have a fuel problem 2001 325i. When my tank reaches 1/2 gas starts pouring out under the car . Basically everything I pump after say 6 gallons ends up on the ground. I did look under the seat and saw the two access points but am curious why the passenger side had the one connection going in the little hole but there is another connection with a 3 pin(actually no pins ) but connects to nothing.
help please. Thank you