This is very true bozo....I've thought about but don't undestand it myself. The way I see it the air pump pulls water in through the intake. Now that there is a void created everything has to fill and the water fills it from the outtake line.....let me try and think of an example.

Think of it as a siphoning thing. If you have a complete circle and you draw something out from one side that something has fill from somehwhere and it does so from the other side due to gravity.

We need X-Crispi or somebody to explain it....they'll understand the theory behind it I think. Or maybe Stinky.....she gets stuff like that.