Can't completely clean the rear of my Volt - advice?

I love my Volt but I find that the rear of the car gets filthy very quickly and easily, and is resistant to cleaning. Maybe it's worse with the car's "white diamond" paint, but I am having a hard time removing all the dirt and grime from the rear surfaces. Anyone else have this problem? How'd you solve it? I'd be interested in hearing what cleaning products (and/or tools) you use that work well for you on this part of the car. Thanks.