ORIGINAL: a cowell
This way you can keep the vent/overflow inside the model, thus helping the scale appearance without any fear of mess to clean up.
So you fill your model with fuel, and the last "overflow" goes into this "inside" tank. And then as your fuel tanks that you filled, swell cause it's hot outside, the fuel from the other tanks purges into this "inside" tank. And then that fuel goes out the hole in your bung in that "inside" tank, and I just want to be sure I've got this figured out...........
YOU HAVE NO FEAR OF A MESS TO CLEAN UP!
I'm not aware of any fueling system that is accurate enough to handle what you are referring to.