There is a drain tap on the bottom of the radiator which only drains the radiator and some of the coolant in the block. To do it properly, engine cool, so no pressure in the system or hot water to scald you. Undo drain tap on bottom of radiator, undo drain tap on block or there will be a lot of old coolant retained in the engine block, remove radiator cap, leave until system stops draining, undo the overflow hose near the radiator cap and lower it so that it will drain the overflow tank to remove the old coolant in it, when it stops draining replace the hose onto the fitting next to the radiator cap. Retighten the two drain taps and refill with the proper Toyota long life coolant (pink in colour) as its not at expensive and much cheaper than having to buy a new radiator or cook a motor from using water or cheap coolant. After filling, I leave the radiator cap off with the engine idling for several minutes until warn or hot coolant starts to flow into the radiator and keep topping it up with coolant as and air bubbles come through the system. In my experience not much air is trapped in the system. You can feel the radiator hose or the top tank get warm as the thermostat opens when the engine warms up and lets the coolant flow around the cooling system and flushes out the trapped air. Top up the empty overflow container with fresh coolant. Job done, just check the coolant over flow container and the radiator after the next drive and top up if necessary.
Trying to save a few bucks by using water or cheap coolant may end up costing you thousands for saving a couple of cups of coffee worth plus the inconvenience of not having a car while its broken down.
