I just mounted a 91 gallon fuel tank/toolbox in the truck bed. When I ordered it I opted and bought a gravity feed kit that drains into the normal fuel filler neck. I guess it's fairly standard but in short you plumb it into the rubber hose that goes between the fuel neck and tank.....my problem is it's to small and the hoses don't fit correctly. Murphy is alive and well.

So my question is can one tap into the fuel filler vent line (at least I believe that what it is) that runs next to the fuel filler neck with a T fitting? I don't care about the legal aspects I just want to know if this configuration will work or would it cause some type of problem.

My other question is at the top side of the aux tank it has a vent outlet in case the truck rolls over which is as this time capped. Should this be plumbed in or what? I'd imagine this would also help with compression/expansion with the weather...right?

Thanks guys....I'll admit up front I'm not the sharpest pencil in the drawer but want to get this right.

 

First you need to un cap that vent! if you don't, when the fuel is trying to drain into the main take it will cause a vac and not allow the fuel to drain until you remove the fill cap to and more.
It only need to be a small tube that exits the truck or bed!

as far as the drain or fill line form the axillary to the main tank,............why not unbolt the factory filler neck and put it on your bench, drill a hole in the metal tube.
now just solderer the fitting in it, and hook it up!

My auxillary tank came with a big ball valve and a garden hoe. The metal part of the hoe, was ground into a hook so the it could be turned on or off from the tail gate!
I have a camper sell on my truck.