Lightman

Tx, that is wayyyy too complicated, no offense. There is no need for all of that. Simply run a hose from the aux tank thru a ball valve (to open or close flow) down and T into the fuel filler neck overflow tube, which is 3/4" inner diameter. It doesn't get any simpler than that, and you don't have to mess with any 'active' fuel lines. If you leave the ball valve open you have the same effect - it keeps the main tank full and your gauge reads F until the aux tank is empty..

Maccandy

Lightman,

What is the function of the 2 fittings on each end of the tank? Why don't they leak?

Lightman

Maccandy that is a darn good question I'm not the type to bs when I don't know what I'm talking about, and I honestly have no clue. I would assume they vent air out when the tank gets really full, as you can hear a hissing noise down there if you listen closely when you fully fill your truck to the brim, or when the main tank is almost full and the aux tank is still filling it. Why fuel doesn't come out of there I have no idea, but it doesn't. If it did, with 51 gals of diesel above it and the valve open it would certainly leak all over the place and stink up the garage etc. Plus I was under there the other day adding the extension hose to prevent any water because of those threads, and there was zero fuel odor or spill/residue, everything was dry and clean.

Iron Mike

They may be vent valves like found on our seawater lift pumps at work. When the pump has been down a while and then started. It vents all of the air out of the line upstream of the check valve. Then when the line (30" piping) is filled up with water the vent seals off with a float. Just a guess, but it makes sense. Maybe a DC tech out there could say for sure.

Lightman

That might be the case Mike, that would make sense since people said they could blow in through the vents and suck air out.. Then again, I doubt anyone is willing to fill their tank to the brim and then suck OUT to see if diesel comes out MMMMMMMM sounds delicious

Regardless, it does not leak.

patrick

I put my RDS 51 gal/tool box in about a year ago,I came out of the aux tank with a short brass nipple,to a brass ball valve,& misc HD brass fittings with a piece of rubber fuel line under the bed.I went into the main fill line on the truck by JBwelding a brass nipple into it.I've been filling up only thu the aux tank,regardless of quanity for about a year,never dripped a drop!My thinking in filling thru the aux tank is, that whether I put $20,or $75 it keeps the aux tank clean.Works great ,adds weight. Pat

Lightman

Patrick I do the same thing but for different reasons. I like having my fuel all go thru the aux tank because it passes thru the racor 2 micron I plumbed in between the tanks. Just gives me the warm fuzzies The extra weight is nice too although its a lot farther forward from the axle.