"the vacuum is exerting a upward force on every molecule
in the straw"
That's just plain wrong. I give up, you don't believe me, you don't believe internet sources, apparently you don't believe in scientific textbooks.
http://www.tpub.com/content/construction/14265/css/14265_206.htm: "Assuming the liquid is water and there is a perfect vacuum below the piston, atmospheric pressure pushes water up into the cylinder
to a height of 34 feet, even though the piston may be raised higher than 34 feet"
Go ahead, try to build a PM without basic knowledge of pysics. Good luck.
You shouldn't apply the electric field. It was just a thought experiment and actually that's part of a scientific process: You have an Idea (like pressure gradient is responsible for floating) and then you try do think of an experiment to falsify your claims (e.g. water columns without a pressure gradient shouldn't let things float).
In this video you can see a drop of water, levitating in a magnetic field. Notice the air bubbles: they are not floating upwards, despite the still working gravity and the density difference. Instead they are behaving like they would in zero-g. (actually they should sink downwards, I guess the thermic motions are to strong or the air itself is diamagnetic to). http://www.ru.nl/aspx/download.aspx?File=/contents/pages/534727/drop2a.mpg&structuur=hfml