There were some studies done on film washing in the 1950s. A 2% solution of sodium sulfite was found to reduce residual thiosulfite in film to zero in two minutes. Film bathed this way, followed by a running waster wash of one minute has less residual chemistry in it than would a sheet of film washed in water alone for more than an hour. This is the mechanism used for the various hypo clearing agents.

Washing efficiency can also be improved by first bathing films in seawater or solutions of common table salt at that strength for ten minutes before a thirty minute wash with running water. One reference in the literature states that a ten minute bath with seawater dropped the residual thiosulfate content to 0.005 milligrams per square inch where after thirty minutes of tapwater washing alone only lowered it to 0.080 mg/square inch.

My preference is to use a hypo-clearing agent for about eight minutes, rinse the film thoroughly twice and then do a very low trickle wash for 15 minutes.