On the water pump cover you will see an oddly placed bolt this is the drain hole. Remove the bolt with the radiator cap on and then when your container is ready open the radiator and it will SHOOT out. Fill the system with 50/50 mix of spirit vinegar and filtered/distiller water and run it to operating temp. Drain again and flush with water then add your coolant
It is not easy to boil these bikes because the radiator are so unrestricted but if you ride v long v tech sections where it will boil you can get a fan kit from GG (I used one from the trials bike - fan rectifier and a handlebar switch)