Joined: Feb 2005
Posts: 13,560
Likes: 44
From: Milledgeville, Georgia
Bikes: 2018 Black Mountain Cycles MCD,2017 Advocate Cycles Seldom Seen Drop Bar, 2017 Niner Jet 9 Alloy, 2015 Zukas custom road, 2003 KHS Milano Tandem, 1986 Nishiki Cadence rigid MTB, 1980ish Fuji S-12S
Power washer? Not only no, but hell no.
I would take the chain off and clean it, take the derailleur off and spay it with Simple Green or something similar and clean it with a rag and a toothbrush. After everything is clean and dry, lube all the moving parts with oil. Short cut method would be to wet a rag with Simple Green and rub the grunge off.