2016 Ram 3500 auxiliary fuel tank plumbing??

I had my 91 gallon tank installed in my 2016 RAM. It's gravity fed into the filler tube. I've had no over flow so far. I had some overflow problems in my old 2008 F-350.

Same as post above. Valve gets left open all the time and no problems so far in the last seven or eight months I've had it.

So how does this work.
Looks like these " drip"systems don't have any thing keeping the fuel back from over filling the factory tank. Fluid level in slip tank is higher than the fuel cap on the truck. Is it only the fuel cap on the truck keeping a spill from happening? It actually has a head pressure of fuel against it ?
Or is there a check valve on the upstream side of the tee into the filler hose on the vehicle?

Sorry Grit. For taking so long to look here again. The fuel cap in the 06 does not leak with the head of fuel above it. I ran all fuel through slip tank so that it was pre filtered to the main. The main fills and air/fumes escape through a valve on it. When fluid reaches the top it must have a floating ball in the breather that prevents fuel leaking.

Thank you for explaining that.
I know the OE fuel tank vents have a check valve on them for rollovers and such.
So the gravity feed system puts that check valve and the fuel filler cap into active duty?
While I believe it works obviously, Im not fond of parts so easily removed like a gas cap being the only thing keeping 90 gal of fuel from spilling.

Are you really able to fill the primary tank with any efficiency through the slip tank ?
I'd think an average gas pump could fill the slip tank before 30 or so gallons gets into the OE tank.

So, reading the other slip tank thread, it appears that there is a check valve in the tee in the filler hose. Makes a lot more sense than relying on the fuel tank vent check valve and the gas cap or whatever seal is in the capless systems.

My 2016 does not even have a gas cap. I was concerned as well but that quickly went away. Most of the time my auxiliary fuel take valve is left open all the time. All I can say is it works and I love having the tank and extra fuel on hand.

Have to say sorry again Grit for not getting back to you about speed of filling oe tank. I used a 1/2 inch hose and yes it is slow. I'll fill tank in box. Go have coffee etc. Go back and fill tank in box once truck oe tank is full if I want to have it all topped up.
One really big reason I love this set up is that all fuel is pre filtered. Change injectors once because of the dirt and water they sell us and you will be convinced.

Don't know why but I have "notifications" checked here but I don't get them??

I should also add. You do not need to spend a fortune on a extra tank. I've installed in my own trucks and a few for others, combine tanks. Massy, Gleaner etc.
Combine salvage my source.