i do a lot of these jobs myself,
2 tips for you
1, keep a seperate brush and don't use the same one that you use for w/cleaning
2, don't waste your pure water, plug directly into the customers outside tap with your pole, you don't require any power either as the water pressure from the tap is good enough, the brush away keeping the water flow going and it will rinse as you brush.
trust me this works
Jay