Most people are familiar with the dryer drum—even if they don't really know what it is called. The drum is that part of the dryer that we put our clothes in to dry. There are occasions where spots of rust can begin to eat into the drum, particularly when the drum has been exposed to moisture for prolonged periods. How often have you left a wet load of clothes in the dryer and forgotten to turn it on? Wet exposure, plus metal, equals optimal conditions for rust growth. If left untreated, you will have a holey dryer drum; all of the heat will escape through these rust holes, and your clothes will have rust stains on them.
Unplug the dryer from the electrical socket to avoid accidental electrocution.
Sand or scrub the rust spots using steel wool or sandpaper. Rust creates pits and these pits need to be smooth, like the rest of the drum areas, to prevent the rust from getting worse and to allow touch-up paint to stick.
Clean the entire inside of the drum to remove all the dust left from sanding/scrubbing. Mild soap and water will work well. Use old rags that can be thrown away.
Let the drum dry completely. You can run your dryer on the fluff dry cycle for a few minutes to dry the drum faster. If you use a heat cycle, the drum will become too hot and you will have to wait while it cools
Apply an appliance paint (see Resources) in the color that most closely matches your drum. Use the applicator that comes with the paint to dab the paint on the rust spots. You may need to add more than one coat, but make sure that you are letting the first coat dry before adding more to avoid drip marks. Allow all coats of paint to dry thoroughly before using the dryer.