Cascadia Fuel Return Shutoff

Figures about the Star, no offense intended, but they were just a little different when we had those 2005s. Long tanks with a narrower profile holding an odd amount of fuel(143 gallons capacity per side IIRC)

To the original poster, you should be able to close the leaking one off and run from the other tank until you get the line fixed, but if you run off the passenger side and leave the driver's side, your fuel gauge probably won't work, I know this from filling one side at a time, fuel in the passenger side didn't register correctly on the gauge until the tanks equalized.

I'd get it fixed as soon as possible, in any case. You need to look at the plumbing underneath to know for sure what is going where, which, if you found the leak, you probably already have,

 

If it's leaking before the valves, you won't be able to fix unless you disconnect the leaking line somehow and cap where it hooks up, or block it like cnsper said.

 

Honestly, I have had the truck I drive for almost 4 years, and never had any of that stuff worked on, not to say it's perfect, but something somewhere along the line made a leak for you.

I drive a 2013 built in June of 2012. Had a DEF leak detected by the shop once, but I never figured it out and it never got fixed that I know of, and I have never seen so much as a drip. It's got between 10 and 11 thousand hours on the engine with around 40% idle, and it gets the job done, despite having check engine lights and dealer shops not wanting to fix it. Just had the DOC filters done, whatever the heck that means, but they burned them out, and didn't have to replace them.

For your truck, If it's coming back from the engine side of the valves, you need to get it fixed correctly, in my opinion.

Whatever it takes.