The plastic plug pushes in, then turns clockwise a quarter turn. That plug should never be removed. There have been a lot of problems with the tank cracking inside where the o-ring seats. That results in a steady drip about once every ten seconds. The only fix for that is a new radiator. We changed a pile of them at the dealership after people opened them up to do flushes. Instead, remove the lower radiator hose. If you have the 3.3L engine, it's right in the front near the tire and easy to get to.
Not every radiator will develop that leak. It depends on which manufacturer supplied the radiator to Chrysler.