Help

I am trying to flush the coolant since I am installing a new thermostat in the car. Now I am a little confused as to how I can drain the water. I removed both radiator hoses but I believe their is still water in the block thats probably dirty as shit. I cant unscrew the plastic drain cock on the bottom of the radiator for some reason (super low bad access fear of cracking?) so how can I do this?

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