Pioneer - The cleaning instructions that come with the GM barrel recommends that you remove both the nipple and the clean out plug when cleaning. I usually throw the nipple in the hot soapy water and let it slosh around in there while I swab the bore. The little clean out plug which is only a tiny thing gets wiped down with #13 solvent and both the nipple and plug threads get a light coating of anti-sieze before putting back in.