My '02 F150 had what appeared to be a spotless interior fuel tank when I change my fuel pump @ 180,000 miles, even sitting for almost a year with 1/4 of a tank in it before I got it.
I had changed the fuel filter when I got it (170,000 miles), and back flushing it after removal did get some stuff out, but as said, nothing I could see in the tank itself. Probably lots of small stuff that can't be seen with the naked eye.