I have an RDS 37gal aux tank in my F350. It's gravity feed and the connection to the full pipe has a check valve that prevents any overflow or leakage. This is our third truck with an aux tank. We don't do marathon days, usually 250-300 miles so long distance isn't the issue. What it does give me though is when we head south I can fill it up locally at the best price around and then make it all the way deep into VA where Liberty and Sheetz compete for the lowest price for miles around. It also assures that we can reach our daily destination without refueling and I can unhook and use Gas Buddy to find the lowest price away from the high priced Interstate exits.
I doubt this tank will ever pay for itself in savings. I just like getting fuel on my terms not the fuel gauge's.
Jim & Deb
50 years happy
2018 Montana 3731FL
2017 F-350, psd,4x4, lariat, c-c, swb, srw