After reading all of the above posts, I've decided that we are all a bunch of granite headed son's of b_____s. We are going to do it the way we've been doing it and there is not one single solitary reason to change it, because it's the way we've always done it.
So.... you guys that are turning your plane upside down to defuel, keep doing it, it'll at least give you big biceps. And those of you that like running and extra line to the tank, keep right on doing it because you like an extra hole in your tank plug and that extra line that can come off of the inlet tube, or get tangled around your pick up line. If you fill your take up and forget to plug that line, it will at least drain your tank to the level of the inlet tube and if you get a good siphon going there, it'll drain your whole tank. But, not to worry, at least it won't be on take off. It'll probably wait until you are going up wind at 10 feet of altitude, right over the runway.
If it ain't broke, don't fix it. That's the spirit.