Found under the following brands:
Annovi Reverberi-AR, Westward, Bostitch, Black & Decker, Craftsman, Devilbiss Air Power, DeWalt, Emglo, Excell, Porter Cable, Speedaire
1/4 turn, that's it! 1/4" MPT Ball Style Drain Cock. Keep your tank from rusting. Replace this if leaking or will not work.
This was a new check valve installed less than a year ago. Due to the tanks not being drained, this check valve failed after less than a year.