Here's what I do. Everybody does it different
I don't wash my top that often. I wash the Mini weekly & I just hose the top down really well with water to remove dirt. When you do wash your top you should use convertible top cleaner (never use carsoap as it isn't good for the fabric & tends to attract dust) & then treat it with protectant. When you wash your top with soap/cleaner it removes the protectant & the top must be retreated . The top must be treated with protectant so it will remain water repellent over time.
I have used the 303 Convertible Top Cleaner/Protectant kit in the past
http://www.303products.com/tech/inde...TOKEN=72020049.
It has worked fine but I have heard good things about a product called Raggtopp & I intend to try it out next time I do a good cleaning
Go here
http://www.raggtopp.com & look under "information center" then "convertible top care", there is a good article explaining a fabric top & how to clean it.