I am changing the fuel tanks on a truck that has a Cat 3406B motor in it. The old style type of injection system. The old tanks had a bung that allowed the fuel to be returned directly into the top of the tank. So there was zero back pressure. With the new tanks I can't plumb the return in the top with out welding in another bung for the return line. The tanks have the fittings half way up the side with internal suction tubes that go to the very bottom of the tank. So there would be the column pressure of the fuel in the tank for the return line/fuel to push against. Will this effect how the system works??? This column pressure would not be much. The tanks are only 25 inches in diameter so the column would only be that much when the tank was completely full.