I too, use Xtol in a 3.5 gallon Kodak plastic tank with floating lid and cover. It does develop grey sediment that coats the bottom and sides of the tank and when replenishing and such the sediment is stirred up. I don't like the sediment, but so far, I have not done anything about it. I wonder if I would harm anything by filtering the tank of developer thru a filter, and scrubbing the tank out with warm water and a scotchbrite pad and then filling it back up with the tank solution of used/replenished developer? I think the sediment is stuff that is a byproduct of the film developing, and does not contain active ingredients, but I don't know.