Hi Fin!
You can spend a considerable amount of time trying to rinse the last of the particles off a conservatory roof, especially if it is a low pitched one. So, what I have resorted to is this. After the last rinse has removed most of the debris, tackle the remainder with a large squeegee on a pole. This final procedure, in my experience, significantly reduces the overall time taken for the clean.
Hope this provides a solution.
Nick