You guys are going off on a tangent here. I only say dirt to mean anything such as particles, debris, rust, gunk, etc., but it's easy to just call it dirt. I think you guys are taking the word dirt too literal.
But I think you're missing my main point. If, for whatever reason (and I don't care how it got there but say it is there), you got dirt (sorry, I can't seem to think of a better word for this) in your tank, it's likely gonna be settled on the bottom. Are you guys saying regardless if you have a full-tank or near-empty tank, if you got a dirty tank, the same amount of dirt can clog up your fuel filter?
Then does anyone care to comment on the following link? Are the people answering the question blowing smoke?
WikiAnswers - Is it better to refill your gas tank before it gets near empty