just buy a regular coolant flush bottle it will be easier - you need some precautionary measures first.
1 remove the thermostat so the water can actually start to move as soon as the engine starts.
after the 1 hour drive you should drain the hot engine with the radiator bottom pipe, now insert a garden water pipe into the engine side and let it flow draining all the rest from the engine radiator, as the design prevents the block from draining, now connect the pipe once again and fill with water and add a tablespoon of meetha soda into a cup of water and pour into the radiator and run for at least 1 hour again to neutralise the acid.
Once done repeat the drain/flush procedure, and verify any leaks - repair as necessary, install the thermostat with new flange gasket and fill with coolant/water and you are done, its best to put in a new radiator cap too.
Before putting the engine into the car, check the coolant metal pipe that runs under the exhaust manifold, if its heavily rusted/corroded renew immediately, its a royal pain to replace with engine in the car.