hooking up a transfer tank to oem tank on the truck
 

Ive got a fuel transfer tank in my truck and was wondering how to hook it up to my truck. Theres no pump on it, but ive heard of people hooking them into the oem tank. I just need help doing so.

Two ways to do this!
1) Put a pump in it and just fill the main tank yourself when needed this is the easiest way to do it.
2) Hook up a transfer pump that runs to your fill pipe breather tube and a switch in the cab to turn it on and off! Just don't forget you turned it on or you will make a big mess if you overfill the OEM tank!
Transferflow makes a system that monitors the main and aux tank and automatically transfers fuel and tells you how much fuel you have!

becareful.. you could fail smog with the tank plumbed together.. read that somewhere.. think on transflow site..

I did Dangerous1965's number 2 option. Now I've got a RDS 60 gallon box/tank combo(before was round 100gal. tank off a semi). I put a 3/4" to 3/8" T fitting into the breather side of the filler. I found the T's in the "help" section in O'rielly's. I think they where heater hose fittings for a ford. They are plastic, but mine have held up for 4 years now.
To be D.O.T. legal you have to have a D.O.T. certified tank, you need to run a return back to the tank in-case you forget to turn off the pump and manual shutoff valve on the output side of the tank.

Unless its a visual thing, it won't cause any codes to pop? I've had mine on for 3 years without issue.

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Do not use the vent tube...a check valve in the tank will cause issues with the aux tank filling the main tank. I know this for fact as this is exactly how I had mine plumbed for a while.

There are probably three ways to do this...electric transfer pump as you noted, a manifold into the filler hose (like a FASS pump), or hook up to the un-used barb on top of the tank (this is a 2nd gen trick, but I don't see why it wouldn't work for a 3rd gen).

I actually took the manifold from my FASS, drilled and tapped it for a 1/4 NPT, and screwed a barbed fitting into it...its worked for me very well.

I cut the rubber fill tub and installed a piece of tubing(1.5"?) with an #6 jic fitting welded to it. I did this on 2 trucks. A 2005 and a 1993. Both tanks , in the bed of each truck, have a ball valve on them. Only problem I ever had was on my 93. The old fuel cap couldn't handle the heat expansion in the summer time right after I filled it up. I replaced it with a new cap and it holds fine now. I did run the vent tube up to the in bed tank on the 93. On occasion it wouldn't drain into the factory tank. This was all done about 5 years ago and has been trouble free. Both pass emissions and no codes to date.