Stones, or gem-polishing abrasive, or whatever, will work on the main surfaces but will not clean out the joints. That probably doesn't matter though, if you keep fuel in it so it doesn't continue to rust.
Here is a page that tells you how to use RS1, and some of the other phosphoric acid de-rusting agents:
http://www.ozrodders.com/forum/viewtopic.php?f=2&t=9381&start=15Note that while the acid eliminates the rust, it does not permanently passivate the metal. Paint manufacturers recommend that you paint exposed surfaces the next day. I don't do the Scotchbrite approach at all, I just paint on the RS1 with an old paintbrush, then leave it for 24 hours. It has dried up by then and does not need to be removed.
