If you're near Troutdale you can bring it over to my place. I just got a fancy new pressure washer and a foam cannon for my nasty car.

You might be surprised with enough patience.

For that type of situation, I actually do bring water into the occasion. I will spray the panel down with UWWA really well, do a single wipe with micro fiber over the entire wetted panel, then wash out the micro fiber in the sink before continuing with the next area. But I do this in the sink in my garage, or in the kitchen sink in the house.

You could use a bucket if you wanted, but it'd be there just to soak/wring out the micro fiber... so you could still avoid needing a hose or making a mess. So you'd just fill a bucket to the top with clean water and you'd make it dirty with the micro fiber.