Flush it just like you would a car. Remove the bottom hose and let it all drain into a large container for disposal later. The way I like to flush is put the lower hose back on, remove the top hose, plug the top hole in the radiator then and just put a water hose in the radiator and run the engine to pump clear water thru till it comes out clear. You may have to remove the thermostat housing on a diesel to get water to flow as it may run too cool to circulate the water.