Why the fuck would you want to spray the interior with a pressure washer?? Wipe it down instead with a dry micro fiber cloth and then a damp one for the dirty spots. Then again with a dry micro fiber cloth. You don't need a torrential rain inside your car!! It should not be that dirty to begin with. This method will just trap moisture behind the speakers, under the carpet, inside the dashboard. Doing this on a regular basis will be very bad for the car. I can just imagine what many of the little mechanical fasteners look like.