My tank gravity flows also, works fine. I plumbed mine in a little different though. I removed the filler neck and drilled a 3/8 hole in the side of it and brazed a brass hose barb to it. Be sure and do it down low enough that it is always lower than the aux tank. Also use hose made for fuel. Ans also remove the plastic insert from the neck BEFORE you get it red hot. I was using a simple inline filter and it would plug up about every 500 gals, but I now have a large spin on fuel filter with water collector on and it is much better. If you can spare the bed space it sure is nice not worrying about find fuel for a good price or out in the boonies. My aux hold 110 gal plus the 35 underneath make for a long time between restroom stops.
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'99 2500,4x4, QC ,LWB ,3. 55lsd ,5 speed, K&N Scotty style, Van Aakan, 275hp injectors, Pacbrake, 4" exhaust, Rhinoliner, 265/75/16s, Pioneer CD player, Isspro boost and pyro on the A-pillar, muffler and resonator in the barn,110 gal aux fuel, transmission filter, Amsoil every where, Amsoil dual remote filter kit, Brushguard, step bars, hideaway 25k gooseneck ball, flame red with agate interior. Getting really BOMBed!!! CM Texas