There is only one tank, but two seperate pumps with pick ups at different depths in the tank (the rear washer always "runs out" first as its pick up is not as deep in the tank so that you do not waste everything on the rear and then can't see out the windshield). One thing to check is have someone stand behind the truck while someone activates the rear washer. See if anything is coming out at all. There is a bit of a problem with the nozzels in the rear wiper arm breaking off leaving a big hole for washer fluid to pour out of. The result is that when you hit the rear washer button, fluid just gets pumped out the back and runs down the tailgate, rather than getting squirted on the glass.