I have a small brush with copper or brass bristles, that resemble, but are stronger and more durable than, steel wool. I've used paraffin wax, WD40, Boeshield rust and stain remover and a host of other products -- all of which seemed to work well.
Goof Off Rust Stain Remover is specially formulated to react with oxidized iron to neutralize and remove tough well water rust stains from most outdoor surfaces. No rubbing or scrubbing is needed. Stains simply dissolve away! It can also be used to remove lime scale and calcium deposits. The Goof Off Outdoor Rust and Iron Stain Remover dissolve rust stains on contact. Spray on and stains disappear. Use it on rust-stained concrete and tools also works on calcium and lime stains. When used as directed Rust Aid is safe around pets and plants.