We need to clean our deck. The deck was put on about 5 years ago and we did not finish it when it was new. I watched the video on the TOH website, it was very helpful and answered most of my questions. Our deck has some really rough places, should we sand these places after we clean with the wood cleaner? What about the underside of the deck, is is important to finish and clean the underside. We have a place to sit under the deck. Do you use the stiff brush on the railings and posts? Thank you for your help.