Great question! I always refer to this great answer from GE appliances. Many customers have successfully removed the rust with this method:
- Fill the detergent cup with three to four ounces of citric acid crystals and close the cup.
- Run the dishwasher through a normal cycle.
- Rinse thoroughly by running the dishwasher through another cycle without the crystals but with a full cup of detergent.
- Repeat the process if one treatment did not completely remove the staining.