If the gun is a caplock, just stick a length of surgical tubing over the nipple and drop the other end into a pan of water, doesn't need to be hot really, pour a bit down the barrel and pump with a wet patch, this will clean the breech, bolster, nipple as well. dry well with patches, pipe cleaners and Q tips or a blow dryer will aide in drying the bolster after removing the nipple, lube with whatever you chose and check for a couple of days with a dry patch to see if rust has begun.