Turn off the water in the fountain while you're cleaning it. Unplug any of the fountain's electrical components.
Read the directions on the descaler or rust remover. Spray it directly on the rusted area of the drinking fountain. Leave the rust remover on for the time indicated on the product's directions.
Use a soft brush to loosen the rust from the surface of the drinking fountain. Wipe away the descaler/rust remover and loosened rust particles with a soft damp cloth.
Apply a disinfectant kitchen cleaner to the fountain's bowl, bubbler and drain. Use a brush to thoroughly remove any grime or remaining loose rust. Wash away the cleanser with warm water and wipe the entire fountain with a clean, dry cloth rag.
Turn the fountain back on, and run water through the bubbler or drinking portion of the fountain for two minutes to make sure that there's no cleaning-product residue inside it.