I had the same problem when I got mine. I tried taking the tank apart and even got a new float and sensor. No luck. Warranty service was poor and very frustrating. I traced the entire wiring of it. No luck. As a last ditch thing I pulled the plug in the harness under the front hatch lid and it looked fine, until I looked closer! One of the little tabs in the plug was bent over. It would not contact but it still allowed the plug to snap together. The easiest way to find the white plug is to trace back from the dash gauge. You can straighten the tab with some hemostats and then plug it all back together. With all I went through trying to figure this out and the hassles I went through trying to get warranty service it would just make my day if this was your problem and it could be remedied as easily as mine was ((once I found it, that is). I agree, the tube is likely just a vent tube as everything on the tank locks in place.