When I replaced the front and side flange of cylinder head and the expansion tank, also replaced Long-life Coolant.
1. Confirm the coolant is cooled completely. After that, remove the cap of the expansion tank.
2. Remove the lower hose of the radiator.
3. Pour the water into the expansion tank for a while.
4. Remove the side flange of cylinder head and pour the water into the flange (to heater hose ) for a while.
(Heter position should be max at this time.)
5. Remove the front flange of cylinder head and pour the water into the flange (to upper hose of the radiator ) for a while.
I used the tap water plentifully but felt the coolant was cleaned up.
After that, reassemble all parts and pour coolant into the expansion tank at max. level.
Start the engine and pour the coolant regularly. When the level of coolant is stable, cap the expansion tank.
Stop the engine after the radiator bigin to operate. Remove the cap of the expansion tank slowly and close soon.
Please note that the coolant is VERY hot and has high presure. So please take care of it if you do that.)
Start the engine again and confirm the coolant level. If the coolant is short, add it again.