my alloys have been manky for about nine months. couldn't clean them - so greasy and dirty that hot water and a sponge doesn't do anything. got alloy wheel cleaner a few months back and it was useless.
tried it again there recently - got turtle wax wheel cleaner - the lad in the shop gave me a free alloy wheel cleaner brush and sure enough it did the trick - spraying the stuff on and then car wash is no use. you need to spray it on and then scrub like mad with the brush - it would be much easier than using a toothbruse cos it was a big enough thing.