The major problem I see in the Ilford wash method is the great unknown - carry over

How much of the previous fix/wash water are you carrying over to the next wash

If you make some basic assumptions on the assumption of zero carry over and then do the same calculations but with even fairly small quantities of residual fixer sol'n then the number of wash cycles increases dramatically.

I am always amazed when I empty a film tank how much liquid stays in at the first pour out, leave it a minute and do it again there is plenty more - and then does not take any account of the liquid on the film and spiral