Soooo, the sediments are usually heavier than the fuel, yes? soo sediments go to bottom of tank.... and where is the fuel pickup line in the tank?? i dont think its at the top of the tank sipping only the clean fuel.... if thats where you all think it is then i wonder how itmight get fuel when the tank is less than full....
yeah that is the point of the fuel filter... and the reason you change it periodically....

 

^^Good point 79percent. I dont like to have my fuel low at all but like 79percent said the fuel is sucked from the bottem not the top and the sediments settle to the bottem. and thats why oyu have your filter

 

I haven't really had time to see how things are set up on Audis, but if the fuel pump is electric and inside the gas tank, the fuel also cools the pump. If the pump runs hot a lot, it lessens its life.