On the metal tanks, two pipes came out just in front of the fairing; one went straight into the wing, just in front of the apex of the fairing, while the other ran along the outside, then went up into the wing ( almost at the back end of the fairing.) I believe that the paper tanks had a slightly different arrangement, with one pipe coming from the back end, but can't (yet) find the evidence. I have a photograph of a metal tank, slung under the Imperial War Museum's preserved P-51D; if it'd be any use, let me have an E-mail address, and I'll send it on.
Edgar