How do you get rust off of vinyl siding?

There are numerous cleaners out there that can do the job; Simple Green and Fantastik are just a few of them. Add the cleaner or detergent to the affected area and scrub it- then you can use a pressure washer to rinse the cleaner off. The website for Vinyl Siding World has instructions on how to use a pressure washer, and the different cleaners that are available.