I don't wash mine. It rains now and then that's good enough. I can see no advantage in an old man climbing onto a roof, soaping it all down and making it slippery to wash it. I just can't see what there is to gain. Nobody can see it. I've managed to get away like this for 10 years on my last rig. This one is going on 5 years. Every time you scrub it you are washing off the top layer of oxidized rubber and shortening the life of the roof. Why not just leave it alone? There must be others that feel this way..
B.O.