Napa or Wallmart carry a bottle of purple power. 1.99 and a little scrub brush very little scrubbing. spray it with hose it will come out black. I use black majic tire wet after it dries and it will be as good as new. I do this about once a month.
Westley's bleach white (tire white wall cleaner) works great for my black top. (the few times that I wanted it that clean)
It also works for tons of other things too. I swear it will take the spots off a dalmation if you need too.[img]images/icons/laugh.gif[/img]