Originally Posted by 4Reak Show

Long post, beware...
Right now I'm in the research phase of the project so it's all up in the air. Here are my thoughts and options from my current Internet scouring:

The Ford tanks seem to be the go-to but upon finding some pictures, they're actually pretty darn big. Which would require potential exhaust relocation or a body lift. Not really what I want to do.

The current idea I found is a tank from a 94-97 Corolla. Only 13 gals but it's a lot smaller and shorter so it would tuck better with a lot less modification of surrounding area. I haven't had a real chance to lay down and do a million measurements to confirm but I'm leaning this way.

As far as transfer system goes, I totally agree. Mounting a stock Corolla tank means a stock pump would have no issue transferring the fuel. The plumbing is where I start having issues especially because CA requires smog and EVAP is a huge part of that.

So my idea is to just have the systems connected but seperatable (if that's a word...) for example, have the EVAP vapor line T'd in all the time since that feeds the charcoal canister and would allow for the second tank to be totally sealed for bugs and dirt or whatever. Also the EVAP system would theoretically still work the same since the entire fuel system would remain sealed, it just draws vapors from a larger "single" container source.

Then there's the filler neck... Land cruiser's from Australia have a crazy dual system filler with a butterfly valve

Issue being this part is like $600. Nope. So I'm thinking of getting 2 junkyard 4Runner filler necks, cutting them in such a way to essentially recreate the above picture and welding them together into a Y... Then puting a large stainless ball valve to the hose of the aux tank. That way I control when I fill the aux tank.

The end game is to flip a switch, have the aux pump fill the main tank through its own filler hose with a secondary small hose HIGHER that runs back to the aux tank's return line. This would mean there is zero chance of overfilling and spilling since any overfilling would just pump the fuel back into itself essentially also eliminating the need for an additional gauge and such. Details haven't been finalized just yet.

This gas tank project is going to be massive. Any ideas or thoughts are welcomed.

Edit:
I was thinking about this all day and looked around under the truck and near the filler neck and had the simplest idea, albeit not the coolest. Have the spare tank as nothing more than a storage vessel. Completely seperate altogether. Run the vent hose for EVAP to a little filter or something tucked away under the truck and have the filler neck for aux tank standalone as well. Then simply have a coil of hose with a 1/4 turn valve on it and a toggle switch nearby to run the aux pump and just refill the main tank via the stock filler neck. Leaves all the factory plumbing unmolested and allows for basic storage of fuel with minimum alterations to the vehicle. Downside being you have to get out to actually fill it up but I didn't see that as that big of an issue really. Sure beats having 2 jerry cans flopping around on the roof.

I also looked into tank selector valves and found that to be whole nother mess dealing with switching the supply and return sources as well as level senders and fuel pumps. Overall, the last idea is the easiest cheapest and simplest way to carry extra fuel without losing storage.