Kevin, From the owner's manual for a power shower Mobile Maid, each fill is 14.5 PINTS. 2 pints per quart and 4 quarts per gallon so 7 quarts + 1 cup means not quite 2 gallons per fill.
From the owner's manual for one of the GE automatic top loading builtin dishwashers often paired with a sink, each fill was a gallon.
From the specs of Robert's 1950 WH rollout with the aluminum impeller, each fill used 7 quarts of water.
From the specs for his APEX Dish-A-Matic,another impeller machine, each fill is 1.5 gallons.
From the owner's manual for the 1956 Hotpoint impeller dishwasher, each fill is 6 quarts of water.
From the owner's manual for the Westinghouse SUC24 series from the early 60s, courtesy of Steve D as in Dishwasher, each fill used 2 gallons of water. These were the ones with the tall Bakelite impeller.