I clean and refinish a lot of decks and I see the advantage of adding on the house wash while I am there. In our area most of the newer homes have ventilated aluminum soffit panels and every time I have sprayed them (usually just to rinse off after a deck job), it looks great for a minute and then all the crud and dirt and dust from inside the soffit washes back out and forms little dirty spots on the soffit where it dries. Usually I end up wiping over it with a towel.
I hate seeing those dirty spots and streaks that often show up under a light or window as things drain and dry.
So how do you pros handle that?