"Why is it my gutters get those ugly black lines, and they were just recently installed?" We are asked this question frequently. These lines are not dirt. They are actually a type of oxidation called "electrostatic bonding". They cannot be removed by any type of pressure washing. It takes certain chemical to counter act the oxidation. http://www.thompsonpowerwashing.com/ has a simple and affordable way to restore your gutters to new condition. The cost is roughly 30 cents/ft for the first floor and 50 cents/ft for second floor gutters (depending on accessability, landscape, etc.).