Hi Roberto - this is what I do (someone will be along later to tell you it's wrong - but it works for me)
1ltr pump up sprayer filled with 50% pure 50% Viro-sol
Gutters n Soffits
Spray brush with mixture ^^ .... extend pole and wet gutters n soffits properly, 5 meters or 15 ft at a time. Turn off water and scrub the mixture into the soffits (as you're scrubbing the Viro-Sol will be eating into the dirt).
I'm really anal about quality so I re-scrub as above with a trickle of water then go back to the start and clean everything on full flow. After that, rinse it all off, again properly.
However well you clean it there will always be dirty coloured water drips - wrap a sill cloth over your brush and run it once under the soffits for the perfect finish.
Good Luck