. . . the fuel always comes out of the bottom of the tank so running it low doesn't make a difference.
Well, I guess you are correct in that the output is on the bottom of the tank, but there has to be something to it.
When I removed the screen, the first inch or so of the screen on the fuel line end, which would be at the bottom of the tank, was completely clogged with the black buildup that seems common. It was the same stuff that I cleaned from the fuel gauge sending unit. So, before I cleaned the screen, the tank was drawing from higher up in the tank. In theory, the car would have ran out of fuel even with an inch or so left in the bottom of the tank. Once I cleaned the screen, anything heavy enough to settle below that line would then be able to be drawn to, or through if small enough, the screen.
I drove the car around a while last night and to work today. In just 60 miles or so, you can already start to see the tiny, black specs starting to form in the inline filter. It may be clogged again in another 2,500 miles.
I am going to see if I can find a local source for some Bio Kleen or other microbe-killing fuel treatment. It is supposed to work pretty well. The upside is that it kills the stuff that is growing on the sides of your tank. The downside is that the dead stuff then sluffs off the sides of the tank and all settles to the bottom. I will probably be back under the car removing the screen before too long.
Anyone actually clean out the gas tank itself? If so, how did you go about it?