Is that the passenger side right down near the passenger manifold? If so its the fuel bowl drain tube. If you look at the fuel bowl theres a yellow lever, first off make sure its closed all the way, secondly open it and close it real quick and see if some diesel comes squirting out of that tube you identified. If it is you need to reseal the fuel bowl drain lever. Heres a link to the orings you need Ford 7.3 Diesel Fluorosilcone Drain Valve O-rings