The correct amount of citric acid placed in the detergent dispenser, dispensed in the main wash (use short cycle of modern dishsmashers which can wash forever in the main wash of the normal cycle) will work on the rust and the calcium-magnesium film which most older machines have to some extent then drain and be neutralized by the first rinse. The owner's manual should give the amount to use.
Decades ago, John was given a Spring weekend stay at their beach house by some friends as payment for his checking out the appliances before the summer season started. The dishwasher was one of the late 60s Westinghouse machines with the blue and white speckeled tub and white racks. It was orange inside from iron. In the short time he was there, the orange juice remaining in the bottom of the glasses started removing the iron stain in the tank where it splashed as he loaded the glasses.
