I cleaned a home the other day that had black streaks all over it. Well on the back side they had a plumbing vent like the one in the back of the picture NOT the pvc. I looked at the home today and everything else is gone, but there is a black streak coming down from the vent? Did I cause this? Was this there and I didn't notice?
Lol I was going to take a pic, but I felt like a clown running through the back yard to take a picture. It looks like an algae stain coming from the metal vent. It isn't rusted colored. Your saying it goes away. I cleaned it 2 weeks ago.