The 2202705300 tank drain bracket may be referred to as a stirrup in your parts manual. This connects to the bottom of the tank on the front right leg via a screw and hexnut. This bracket securs the tank drain tubing and manual ball valve to the receiver leg.
This was commonly used on several Atlas Copco, Chicago Pneumatic and Quincy air compressors.
The part number may be displayed in your manual as 2202 7053 00, 2202-7053-00 or 2202705300.
2203 0387 00