1) every 6 months,
2) first vacuum dust
3) do in bathroom with two flat bucket
4) soak radiator in a bucket of cold water with dish soap for 5 minutes (in the past I did a mistake, should not use warm water)
5) rinse and run through bucket of water (recycle bucket of water to another bucket. repeat)
6) rinse 2nd time with clean water again like step 3
7) tap rad slightly on your tigh to get rid of water.
8) Wipe excessive water with a towel (i have a dedicated towel for my rad only)
9) left dry in cool air or to use a home fan to blow dry. (never place rad in hot sun or use hairdyer)
10) once dry place it back.. can see temp difference (before and after clean), normally 2 to 3 degrees better.