The John Guest Stem Elbow P1220808S is the replacement part number 33503505 for Hydrotech reverse osmosis models 12301, 12302 and 12303. The Elbow with Stem connects the flow restricter tube to the RO manifold.
This fitting is made by John Guest, and is known as the Speedfit Plug In Stem Elbow Quick Connector (part number PI220808S). This is a genuine John Guest fitting.
See the Hydrotech RO Manual for more information.