If you apply soap and use a brush, you won't need a pressure washer and you don't need to cover anything up. Everything under the hood is designed to be splashproof, and honda electrical connectors generally have o-rings to keep the water out. Just rinse it all out gently with a hose. I've been doing this for years with no problems. If your crx has trouble in damp or rainy weather you may not want to do it this way though.