I've just looked in my copy of Monochrome Darkroom Practice by Jack Coote (1982), which has the following about film washing:
It is often mistakenly assumed that efficient washing can only be achieved by using large quantities of water for long periods of time. But, as G. I. P. Levenson has pointed out, it would be possible to wash 1000 feet of motion picture positive film to archival standard in one litre of water, provided that the water was used efficiently. He has also reported that: "Excellent washing of a processed roll-film was achieved in a spiral tank by giving just three half-minute changes of cold water and agitating well during each period. The tank was just emptied after each wash with no attempt to drain thoroughly. After the third wash, the film was wiped before hanging it up to dry."
Now, without looking at the original material, I can't offer any advice about what excellent washing might be, but Coote goes on to mention that Levenson proposed that there be two levels of 'safe' washing - one for archival, and one for commercial use.
As his target for adequate commercial (my emphasis) washing of film, Levenson aimed at diluting one hundredfold the concentration of thiosulphate solution in the image layer when it left the fixer.