Soap being bad for cast iron pans is mostly a myth these days, unless you go overboard with soap. Most soaps don't contain the ingredient that strips away the seasoning anymore.
http://i.imgur.com/FUshe.jpg http://i.imgur.com/o3JZO0i.png https://i.imgur.com/E5QxHCe.gif
http://www.gamefaqs.com/boards/1170-but-wait-theres-more