In reply to message posted by Retired plbg:
… When you put it back you need a union and a nipple…
Just to clarify what RP means by “a nipple:” you will need a special nipple that has reverse (male) threads on one half or a more commonly available special coupling, with reverse (female) treads on one half. These fittings allow you to tighten the pipes together by turning the special fitting in one direction. The union is the easiest way to go, but the reverse-thread fittings may be required if you plan to bury the connection in a wall or you are running gas.