Joe I have had that very thing happen to me on my F22.
I have 2 saddle tanks that feed into one header tank then into the UAT. I also have dual vent lines and vents. I topped off the plane then walked away for a while. With the main hatch off the sun was shining directly on to the tanks. The fuel expanded and syphon out of one side and drained almost everything out of one of my main saddle tanks. I like having an extra drain for the bigger engines with no T fitting. But this is something you need to be aware of.
I don't top the tanks to the very top anymore. Since I started that I have not had a problem. This only applies to planes with dual vents. Also Joe even if you have separate feeds into a header tank it will still happen thee same way. The fuel just has to travel a little further to get out.
Country boy something you can try is when taking the taxi tank off pull one line off the plane. Then cover the vent so the other tank that's plugged in still feeds the engine. Then remove that side while you have your finger over the other vent. This would fix your problem. Or just use a single vent with a T. But I like 2 vents myself.
Last edited by gunradd; 12-03-2013 at 09:11 AM.