Those relief valves, like the ones on water heater, are convienient to use for quick draining but the rubber gaskets in both get hard after a while and when they sit against the sealing surface they get imprinted. then when you use them they dont always reseat in the same position and the previous imprint will cause a leak. I always caution people to not use the relief valve in this way you will develop a drip/leak. Instead put a loose male quick connect in somewhere, or better yet one with a ball valve and drain down that way.

Its always nice finding all the parts to something and reuniting them. Or it was after years of small kids im getting board of the feeling as everything they get they almost always scatter to the four points of the house.