This is the fresh water drain. The low point drains are identical but are currently heat taped and insulated, so you can't see them. Get the valve with the threaded female to match the original male threads. If I recall, it's 1/2 inch but I can't swear to that.
Unscrew the original cap then screw this one on. If you're quick, you can do it without draining the tank and lines (I did). I had to use some pliers on mine to finalize the tightening because it wanted to leak. But it doesn't now. These have been in place since early December and do not leak.