There may only be one bleeder on the hydrovac in 1950 - all I know about your year (1950) is
shown in this multi-year Shop Manual.
The hydro-vac in my 54/55 GMC 2-ton did not work correctly until I followed the suggestion for a pressure bleeder (Chev shows pressure for 1951 and later, so you should be OK) and the bleeding sequence shown in the GMC maintenance manual. I think the GMC sequence might be different - maybe due to the location of the hydrovac?
