Here you go Nath ... works every time for me
1. Scrub each wheel well with a cream cleanser like Cif and rinse well
2. Grease hubs well or use a good quality PVC tape to mask them up (or both - tape then grease)
3. Soak in neat bleach and leave for 24hrs
4. Remove each wheel and repeat step #1
5. Check hub masking and repeat step 2 if required
6. Return to the bleach and leave to soak for another 24hrs
7. Repeat steps 4, 5 and 6 until you're happy with the finish
Steve