A good tip for rad cleaning is bung the hose holes and pop a dishwasher tablet in the top.
1/2 fill with boiling water, fit cap and give a good shake and turn.
Do not block breather tube, allow the water to flow out this will also clean the breather
Leave water in for 10 mins or so and then flush rad with fresh water.
Its amazing the crap that comes out.
Hope this is of help