cleaning is important, but there is no need to sanitize since it is pre-boil. It is a good idea to keep the rubber gasket that was probably on the inside of your cooler to use with the new fitting, so that it seals up tight. The standard way the drain plugs fit onto the cooler is essentially two threaded fittings that cinch together, and then a gasket on the inside wall of the cooler. Looking at the inside of the drain, see if there is a way to put a large screwdriver / knife / pliers in there and turn left-wards, once it's loosened, you will need to hold the outside fitting with your hand or pliers, this should completely remove the bulkhead, so that you can install your own, using the original rubber gasket.
