Just going to throw this out there - just did this a few weeks ago. The plastic on ours not only had some residual wax, but was also FILTHY. Just a wash didn't come close to making it look good. Personally, I think all of the products mentioned in this thread will do the trick, but what is important is how it is applied. Just like washing, simply rubbing it over the surface wont cut it.
I took a medium bristled brush, Mother's Back to Black (which I have been using for about 12 years now), and went to town. So, not only did it really clean deeply, but the Back to Black gives a nice sheen and protectant. What I like about it as well is that it is not overly greasy.
Anyway, in short, take a brush and elbow grease to it, and you'll get the wax and dirt out very well.