I used a pressure washer. I noticed my siding had several holes on the bottom of the individual pieces. I assumed they were there for drainage in case water got behind the siding and air flow to dry any condensation. I did spray the seems, because the ones on my house are overlapped similar to roof shingles. I can spray one way and no water can get in, but the other way a lot of water will get in and start to rip the siding off. On the areas too high to spray I used a stiff brush on a long pole and simple water.