Hello everyone my name is John. I am in need of some advise. I tried to clean some gutters for a customer and the gutters had (shingle oil) or something to that effect that has stained the gutters with black streaks. The house is only three years old but it looks like his gutters stopped up and what ever chemicals are on the shingles stained the gutters. Bleach will not get it. Any advise to get this in a cost effencient manner. Thanks for the help.