Coolant flush

Just remove the lower hose at the radiator. Saves time & money.

I am not very experienced with Chevy but sometimes when I come across one of these plastic screws that won't come out, I order a new plastic screw, heat a screw driver and let it melt into the screw, the cold plastic cools down the hot screw driver and allows the screw to be easily unscrewed, then replace the screw with the "new" screw and properly tighten the screw.

it doesn't turn it pulls out

Why would you even mess with the drain cock when all you need to do is remove the lower hose!