Remove water from the bird bath if rust is occurring where water is located.
Pour 1/2 to 1 cup baking soda into a separate bowl.
Slice the large potato down the center so there are two nearly equal parts.
Dip one slice into the baking soda so that it's thoroughly covered in baking soda.
Scrub the rust-covered portion of the bird bath with the potato. The combination of potato and baking soda safely lifts the rust from the bath.
Repeat Steps 4 and 5 with the second potato slice, if necessary, until all of the rust on the bath is covered.
Pour a few tablespoons of water into the bowl, then dip the toothbrush into the solution so the bristles are fully saturated.
Scrub the bird bath with the toothbrush to completely eliminate the rust.
Repeat Steps 7 and 8, as needed, until all rust stains are removed.
Wipe the cleaned area of the bath fully dry with a soft cloth.