Turn the water supply to the refrigerator to the off position. Unscrew the screw that is holding the copper water tube in place. Slide the tube out of position.
Hold the tube upright and pour 3 cups of vinegar into the tube. Keep the tube over the reservoir to catch any overflow. Leave the vinegar sit for 5 minutes.
Using gray tape, tape the copper tube to the back of the refrigerator to keep the vinegar draining down towards the reservoir.
Depress the ice dispenser to expel all of the ice and allow about half of the vinegar to flow through.
Depress the water button on the water dispenser to run the vinegar through the water supply pipes and tubes. Keep the button pressed until all the vinegar has ran through into the reservoir.
Dip the toothbrush into the vinegar in the reservoir. Scrub the spout that the water comes through with the old toothbrush. Continue using the toothbrush in the corners of the reservoir.
Remove the reservoir tub. Rinse well with warm water. Replace.
Place the copper tubing back in its space. Turn the water back on. Run fresh water through for a few minutes to rinse all vinegar out.