The Trig you are referring to is called "The Entrance" TS10475 Last inspection was August 16, 1077. Worth noting that all trig stations on reservoirs are no longer maintained or used due to variation of position caused by the variations of water temperature and volume inside the reservoir.
Official position is 33° 21.353'S 151° 29.693'E
Information from the Lands Dept in NSW is now on a pay for use basis since it was incorporated into the Finance Dept.