once in a while I lay the TORO walk behind on its side and pressure wash, staying away from areas where the water can penetrate, like the transmission etc.. Then start it up and run it a few minutes to sling the water out. Then spray it with WD40 or something that displaces water. Once in a long while I wire brush and lightly sand the bottom, and spray it with a couple coats of matching Rustoleum. The only time I know of that low pressure water will wash grass off is when it is still soaking wet, and it is still going to leave a film unless one brushes it with soap and water. Think of a dirty car with mud on it. Once the grass dries it turns hard and takes a while to rehydrate. Sometimes I just use an old putty knife on it to knock the old grass off. Depends on my mood. I do pull the blade and the blade holder off, glass bead and paint them periodically.