That's just way too funny!!!! I don't mind plumbing when it's new either but the one house built in 63 was A thrill, everything from the main to the bath tub wouldn't seal so it was always dripping when you were working on something.
Tank plumbing is another story though, I would do all your plumbing and covering if you would do all my sanding. I have been known to mention before how much I don't like sanding.
Brad got right to the point and someone else mentioned crossing the fuel lines, I have done that A number of times with my three lines, either not marking them when I assemble the tanks or forgetting what the markings meant, even done that with color coading too.
Most the time when I have A bad line inside the tank it is broken or has A hole in it right at the spot where the brass tube ends and the line begins. The last few years I have been soldering barbs on the inside brass tubes and smoothing them out with A rubber wheel and this seems to have cured that little problem.
I have had poopyugler in my carb before but most the time I have found A broken line inside the tank.
Do the easy thing that Brad said first and if it isn't crud then go straight into the tank. I keep extra caps and plugs in my building box just for those nasty little problems.