We did one recently, was a right state, but this is how we do um.
Turn flow right up, soak it all properly and ideally leave for a min or 2, then give it a going over. Again keep the flow up.
TBH we slightly under priced it at £30 as 4 bed detached, just front of house, took at least 40 mins, which isnt too bad as did windows as well and next door but compared to just cleaning windows was way way harder, obv depending on the dirt content. Ive got some pics some where if i can find them