I use 2 techniques.
If I have a lot of time before I need them, I stack them outside and let nature clean them up then use a wire brush and a fox tail to remove the remaining dust.
If I need them right away, I will place them in a large pan and use a pressure washer to clean them. It is messy and you are going to get wet but it works real well.
I do not like to wax them until it is close to the time that I need them because our weather is so warm that the bugs get back into them.
When they need to be waxed, I use a 5" firm roller dipped in wax at 170 degrees and roll both sides. This goes very fast.