I looked on the website you mentioned. There is nothing detailing exterior gutter cleaning to be found.
My questions revolves around the statement : You first clean the gutter primer, rub & rinse , liquid dish soap.
What are you referring to as 'Primer'?
Rub and rinse with what?
Liquid dish soap is not a go to product for cleaning black streaks off of gutters.
So, can you get a bit more detailed in your instructions?
Rod