Spray WD-40 on the rusted areas of the icing tips. The lubricant breaks down the rust so that it can be removed easily. Let the tips sit with the lubricant on them for two minutes.
Scrub the rusted areas of the decorating tips with a toothbrush to remove the broken down rust.
Rinse the rust and lubricant from the tips. Wash the tips in the dishwasher before using.