I use "409". It's a spray-on as it's sold, but I pour 4 or 5 bottles into a bucket, add just a little bit oif hot water, and use a medium bristle scrub brush on a broomstick to scrum. Rinse thoroughly, let dry, then use the spray-on roof protection, working that in with a softer bristle brush.
I use the same "409" treatment on my awning. Works great!
2014 RAM 2500 Laramie 4x4 Quad Cab w/Cummins Turbo Diesel, 2009 Rockwood 2607, and 3 'yaks!
300W of Suntech Solar, a Rogue MPT-3024 Controller, and a Xantrex PW2000 Inverter