Pour lemon juice or white vinegar over the spray arm until you cover the surface. Let it soak for five minutes.
Clean the surface of the spray arm with a sponge, scrubbing any stubborn areas.
Pour four cups of white vinegar or lemon juice in the bottom of the dishwasher. Run a cleaning cycle with empty dish racks, allowing the dishwasher to flush the entire surface with the vinegar or lemon juice.
Stop the dishwasher cycle before the drying process begins. Prop the door open and let it sit for two to three hours.