veh 85 td 185k pri filter changed often as it gets restricted with black crud. ive tried additives but had little if any success. last prob was severe enuogh that it was necc to blow back thru line as tank strainer if equipped with or line was plugged to the point that elec lift pump couldnt pull fuel. this has been a prob in tropical climates [so fl] for a long time.does anyone know of a solution [chemical] rather then making tank removal part of maint. procedure. many thanks for responses regards butch