The main problem with the theoretical analysis of washing in running water, is that you can make two fundamentally different assumptions, which will lead to radically different conclusions.
Assumption 1: The process is a gradual dilution, where the incoming water is perfectly mixed with all the water already in the tank. This is the worst case.
Assumption 2: You have perfect laminar flow past the film, essentially a first in first out condition, and the incoming water simply pushes the old water ahead so the film is always exposed to fresh water.
In reality, you will have a mix of these mechanisms, and you will have to experiment to find how efficient your method of washing is, depending on tank size, flow rate, and flow conditions.
In contrast, a fill, agitate, and dump cycle is easier to analyze, since the agitation will ensure that the thiosulfate is more or less evenly distributed in the water at any time.
Originally Posted by brianmquinn