TGC,<p>1) It doesn't matter what you use, As long as it doesn't have a motor or an engine on it, there is no way you'll hurt the underside of your deck.<p>2)You can spray diesel fuel or cooking spray or silicone or whatever works for you under the deck after you clean it out good. It doesn't actually keep the $hit from building up under your deck, but it does make it a hell of a lot easier to clean off<p>Those other guys were right about the pressure washers, SCRAPE FIRST, and clean off as much as you can if your going to use a pressure washer. If you don't it just makes a mess.<p>And heres a tip for after you pressure wash ANYTHING with moving parts: Grease and lubricate everything after you wash it. I know the grease don't look pretty on your front casters and the grass sticks to it, etc, but it'll save you a lot of money down the road. <p>Go by the book as far as your maintenance goes and you'll be covering your ass. Also keep good records so you keep up on maintenance and schedueles.<p>Good Luck and happy cleaning!<p>----------<br><a href="http://communities.msn.com/guidosequipmentpics/">"Guido"</a><br>David M. Famiglietti