The black streaks, normally are a combination of fall out junk from the sky & oils from the sealants used to seal the joints in the roof, so washed down by the rain.
As noted above, the dish soap, if you use a good quality type, take a wet rag & squirt some onto the rag & apply it full strength to the streak, let it sit a few minutes & then wash off, normally it will remove the streak.
By the streak containing oils, most regular soaps wont touch the streak & any other harsh/strong type of soap will harm the Red Max.
Neil
