Yeah, looks nasty, doesn't it? It's balsa sanding dust. I forgot the thing was sitting there and didn't cover the engine while sanding something else. I shoulda cleaned it up before I shot the picture but remember it is an .020, that's a real close closeup, in normal vision you can hardly see any dust on it. See the "normal vision" below, shot at the same time.
I like that, "destroy the integrity of the tank". Seems like I got that tank from you, didn't I? With the hole already in it? Anyway, I felt the same way at first but the stock tanks are pretty much worthless when you think about it, too small for more than a couple minutes' run, won't feed well inverted, tend to leak...butcher 'em, I say! Since I was shown the above integrity-less fuel system works, I'm a True Believer.
--Ray