Will this plumbing diagram for my aux tank work? MS Paint included
 

I ordered a 45 gallon RDS transfer tank that I would like to have plumbed into my factory tank. Gravity feed is a no go for me. I want a pump that I can control with a switch inside the cab.

One of the potential problems with an inline pump is accidentally forgetting it is turned on and then over filling the stock tank. I am wondering if I may have solved that problem. Take a look at my diagram.

Could I safely route the vent from my factory tank to the drain valve on my RDS aux tank? So if I left the pump on by mistake, it would just circulate the fuel back to my transfer tank.

I would however need some kind of one way valve so it would not gravity feed from my aux tank drain through my stock tank vent.

Here is the diagram. Would this work, both safely and reliably?

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And if this is a good method to set my aux tank up, what inline fuel pump and filter should I use? Should I look at inline filters that also include a water separator? What one way valve should I use I the vent line? And what should I splice into the factory filler neck with? I do not have a welder. I've seen the RDS kits come with a nice connection T for the filler neck but the kit is $80 bucks and I would only need that one part.

ETA another thought just crossed my mind... Would the one directional valve cause venting issues with the stock tank?

Before I comment let me say that I don't know. ( yes I tell my wife im always right but lets keep that between us) my first thought that comes to mind is the factory fuel cap isn't air tight. so if you were to forget and leave the switch on then it would overflow out of the factory filler cap before it would ever be pushed up the vent back to the aux tank.

With that being said My father in law has an aux tank with a gravity feed and it does not over flow from the factory filler cap. but if you remove the cap it will certainly come pouring out.

Just food for thought. My .02 cents for whatever it's worth.

hmm didn't consider the fuel cap not being air tight.

any other comments?

I'm seeing a problem with the one way valve. There will be constant pressure against that check valve that the diesel tank vent tube will have to overcome. The factory filler neck has a vent tube attached that dumps the venting fuel and splashes back into the filler neck. You will have to plug that off with the way you have this drawn out. With that vent tube plugged any "burping" of the diesel tank will be out the filler cap if the pressure against the check valve can not be overcome.

That directional valve will not allow the lower tank to breathe or equalize the pressure in it. When you put fuel in the upper tank, you will add about 3.4 lbs per inch of fuel depth in the upper tank. You would need to have more air pressure in the bottom tank than the weight of the fuel holding the breather valve closed in order for the breather to be effective.
In this configuration, there is the possibility of the pressure blowing the valve internally, and back filling the bottom tank. If that happens, you will find out when you try to fill the bottom tank and everything from the top tank comes out of the filler neck.

My advice ... move the air inlet to the top of the both tanks with no valve. That will equalize the tanks (pressure wise), and keep the separated in case of puncture. You can then fill the lower or the upper tank without risk of back flow out the fill neck. You are using a pump anyway, why risk it?

Put a particulate filter in line (before the pump) from the top tank. That will capture most of the dirt that will damage the pump. You should have a filter before the truck pump that will capture water and small particulates anyway.

could consider using a timer switch,but you would have to estimate how long to set timer.

What if I just routed the factory tank vent into the top of the aux tank? That way I wouldn't need the one way valve and it theoretically wouldn't have any resistance. Other than going up hill for a few feet. Would that work?

ETA I just crawled under the truck and it looks like I wont have enough hose to splice into for the filler neck since it's all metal. Guess I will have to get a shop to weld something on for me. Any idea what I should use?

Answering your question with my quote from two posts above. Yes, this will work very well, just make sure you have no traps in the line (a continuous down slope, with no pockets to trap liquid).

do the hutch mod. Install a female "T" before the inline filter, with ball valves on each port. The other port feeds the factory pump. When you empty the factory tank, jump out, close off the factory tank ballvalve and open ball valve to aux tank. This way, your not messing with really anything. and both tanks are fed to the inline hutch filter, and one less pump to worry/wire up.

Here is what i did. I control flow from aux and main tank with a universal electric switching valve. (autozone carries them) (pollock i believe they are called) . The whole set up is made to work as two separate systems sharing 1 fuel pump and a spin on filter. The return line is setup to drain to whatever tank is being used. Its been a long time since i did this setup so i cant remeber exactly the plumbing but the switching valve comes with pretty good instructions. So when i hit the switch the valve draws and returns fuel to the same tank. I added a float to my aux tank and spliced it to the factory harness. The aux tank is simply vented to atmosphere via a welded bung with a hose attached to it and routed to the bottom of truck.
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That will work fine make make sure you have a rollover valve on your aux tank vent. You have to pump the fuel gravity does not flow enough, my pump moves 8 GPM even through the water seperator and filter.

Why would a gravity fed system be a "no go" for you? Mine works outstanding

Don't over-think it too much. I ran mine as a gravity system for several years but switched to an aux fuel pump and a switch on the dash. I have the RDS 91 gallon and I run a line from the pick up tube to the Holley electric blue 110 gph fuel pump that is mounted to the inside the bed. The hose then routes from the aux pump, through the rubber grommet in the bed and down into the fill tube using the RDS adapter kit. I don't use extra filters and have never had an issue. I flip the switch, let it run for 15-20 minutes and then switch it off.