Rust is a common problem for hummingbird feeders, especially if they are made of metal. Rust can be unsightly and can also contaminate the nectar, making it unsafe for hummingbirds to drink. There are a few different ways to remove rust from a hummingbird feeder, depending on the severity of the rust.
For light rust, you can try using a mild acid such as vinegar or lemon juice. Simply soak the feeder in the acid for a few hours, then rinse it thoroughly with water. If the rust is more severe, you may need to use a stronger acid such as muriatic acid. However, be sure to follow the directions on the product label carefully, as muriatic acid can be harmful if used improperly.