I was thinking about this today as I poured flat pop out of a two-liter bottle. When I held the bottle completely upside-down over the sink, it seemed like it took forever to empty, because air bubbles kept "gurgling" up into it, slowing the descent of the liquid. So, have any studies been done that would determine the best angle? I realize there are a lot of variables here: the size of the bottle's mouth, the viscosity of the liquid being poured out, etc. I assume that the best way might be an ever-increasing angle, relative to the amount of liquid left in the bottle, just enough to eliminate the "gurgle" factor, but that's just a guess. Any opinions on this?