Cattle I have installed several FASS systems and I have to say everyone I've done including my own there has been this black stuff in the tank, clogging up the in tank pick-up screen, and still in the tank at various mileages on customers trucks. This maybe an issue, I think persoanlly and someone correct me if I'm wrong, but I think its part of the maching so to speak of the black plastic the tanks made of, or where the factory drills all the holes in the tank, not cleaning them out good, I dunno, but what I do know is I've installed several FASS systems with pick-up tubes in the tank and every truck I've seen has had this problem, food for thought... .....