I think it's called gutter buster?
But I only clean the insides. I think you will find the info easy in the Powerwashering area vs gutter cleaning. It's similar but quite a few that read this forum are into inside of the gutters more than outside. Outside is more in tune with whole house washing. Sorry I could not answer your question.
Does anyone know of a cleaner that will clean black streaks from rain gutters?