Garden Hose is the best way and use some cleaners if needed. I saw a guy clean his radiator at the car wash once. I said be careful, he said he knew what he was doing. Then I heard him cussing. Wait.......Wait for it..........Yep he destroyed it! HA guess he did know just what he was doing (buying a new radiator)! Your location and offroad activities dictate the cleaning process, but never use a high pressure water or air. It WILL bend the fins and then you will be using a radiator comb to fix it if you even can. I like to spray a cleaner into the radiator if needed and just flush, flush, flush with water. I've seen some that were required to be removed and soaked in tubs of water to be cleaned being caked in mud/clay. Of course cap the inlets and outlets first. Clay, its a terrible thing. Probably even worst than sand for equipment.