Someone above questioned whether there was a misprint or error in Ilford's method of washing. I'm going to try to clear this up a bit.
The Ilford method, as posted, is correct for film. It represents a methodology devised during water shortages in Britain many years ago and represents the low end of washing. It also represents only one type of water, that used at the Ilford site and a limited combinations of film and fixers.
In this article:
http://www.largeformatphotography.info/unicolor/ilfwash.pdf posted above, it shows exactly what I describe, and that is that the level of hypo approaches a low level and then the rate of change during washing slows down and finally stops, leaving some residual hypo and silver behind. This always takes place, and as Ctein has shown, some hypo is needed for optimum stability.
Mason shows mathematically that this whole scenario is to be expected by laws of diffusion, and that the most efficient wash is in running water with agitation. So, he describes the high end and recommends it. He is generalizing for all films, fixers and water supplies - which I might mention is what I'm doing as well.
Why do I do this?
Since water differs all over the world, and many films and fixers are in use, it is impossible to tell whether the low end is sufficient for any given condition and that is why I err (if I am indeed erring) on the side of caution and give you the high end condition. Mason, knowing all of these variables has suggested the high end as well. Besides, this high end method works for film and paper both with the appropriate times being used!
In any event, I always say "use what works for you". I also say "test". So, if you are determined to use a given set of conditions and it includes the Ilford method, then I suggest that you test your photo material for retained hypo and retained silver both. If it fails the test, then your conditions are not proper.
So, if any of you are using the Ilford method, and have not tested your film or paper for residuals, then you may (may) be in for a surprise. Actually, I used that method when I was a teen, and today (over 50 years later), I have prints and film that are beginning to stain. I was taught at some point along this line to use the long wash in running water and those negatives and prints that were washed better survive without stain. That has made me sensitive to this problem.
You see, when I started doing photography, I was told to stop wasting water, so I used the 3 short wash method which was known even in the 40s. This is nothing new, just the times and numbers of soaks vary over the ages. So, when I went to work at Kodak I had the chance to talk to some of the experts there about wash and learned how to do it their way and how to test for it. I also learned the reasons which were related to the types of film, water and fixers being used by the customers.
I hope this helps a bit to explain things from my POV a bit better.
PE