To clean it, take the 2 screws out
(Now comes the hard bit)
Place it on the floor, with the screw hole facing you.
Next, use a quick blow from your knee an hit the ball hard.
You should hear a popping noise
Now the casing will be loose an with abit of persuasion it will come free.
Clean with a tissue and put back together.
This technique works, trust me (Plus it says so on powerball site)
Can also use a vice to do the popping tequinique, just put it in a vice an tighten vice till you hear the casing pop and seperate (Y)