There are special coolant flush machines which are designed to remove the old coolant and refill the cooling system with new coolant. It is also possible to drain and refill the coolant only. Most radiators have a drain port which can be opened to allow the coolant to drain out. Once as much old coolant as possible been drained from the system then new coolant is added to the system. Whenever the cooling system is serviced the proper coolant mixture must be used. Old coolant is considered hazardous waste and must always be disposed of properly.