I've noticed there is a fair bit of resistance coming from the pulleys in the rear derailer while spinning the cranks backwards.

I'm well aware that using a pressure wash on a bike is a rather terrible idea. What if I pressure wash the frame, chain and derailer at a safe distance first before removing the chain and derailer for a proper degrease?

Or should I just remove the chain and derailer in the first place to get to work? What would be the best way? Using some sort of shallow bin filled with degrease and a brush?

There are a lot of crevices and what not such as in the front derailer as well which have been caked in dirt and grease for a very long time. Any suggestions would be much appreciated.