When you install that nipple you should put some sort of sealer on it. They make a teflon sealer in a tube (kinda like pipe dope but consistency is a little different) that is available at Napa that works best. If you can't get it regular old teflon tape works too. Putting sealer or teflon tape on it also acts like a lubricant that will allow you to tighten it better without stripping it. Also makes it easier to take out if need be.