Bill,
I might have misstated the use of vacuum with the earlier (54/55-1st truck) foot-lever operated windshield washers with electric wipers. There was no vacuum and no electric pump on the 54/55 Commercial vehicle (truck) washer unit.
My comments/questions are directed to the use of an electric pump in the 57 truck - it looks like your photo shows a non-electric foot pump (as used in 54/55).
You are correct that a vacuum hook-up is not apparent in most of the diagrams in the instructions you linked-to; however, electrical connections also do not seem to be apparent in those diagrams.
1954/55 truck (and car) cable-coordinated foot-pump operated windshield washer Note the similarieties between the 1957 unit and the 1954/55 unit (at the link above) The cable connection (the foot-pump co-ordinator) to the 1954/55 electric wiper motor is just like the set-up shown in the 1957 truck diagram.
All 1954 automobile washer units used vacuum to the water reservoir and sometimes to a vacuum cylinder as a co-ordinator (when equipped with a push-button control as apposed to a turn-knob control).
