How do you gain access to radiator drain cock

Pull the lower radiator hose instead. I haven't opened a petcock since the mid '90s when we had a rash of failures. They almost all use plastic radiator tanks with plastic petcocks with a rubber o-ring. Opening the petcock causes the plastic to crack where the o-ring pushes against it to seal, then you have a constant drip, about once every five seconds. The fix is to replace the radiator. Safer to just pull the hose.