I wouldn't be without my pressure washer , i've had one for about 10 years . Cheap as chips now .
Blast off any loose dirt first .
Then run a length of hose from a large container , like a 25 litre fermenting bin , fill it with water and a couple of capfuls of shampoo = lots of suds
Then just wash as normal with the 2 bucket method .
I usually spray the alloys with fairy power spray and leave to soak for 10 mins while i set it up . Then power wash the wheels and they come up a treat . Especially if they been waxed or protected with AG super resin and EGP , or Wheel Guard from carwashnwax . Just tried the Blue Rim Wheel Cleaner that i won from carwashnwax . I can recommend this as well . As soon as i sprayed it on all the brake dust started to run off the wheels .
http://www.carwashnwax.com/