Ed, I use distilled water for all the steps in film processing including the final rinse, thus the water economy is important for me. I started with the procedure outlined by Ilford in their data sheets (drain/refill several times). But I wanted to be sure it gives an efficient washing. I did some calculations (a simple task about several dilutions) and found that five steps are enough assuming 2 conditions kept true:(posted 8278 days ago)1) The time for each step is long enough to allow the diffusion process to be completed
2) The amount of the solution carried to the next step is minimal. The calculation showed that this amount greatly affects the wash efficiency.
Practically (for 2 reels tank) it means:
1) 1 min, 5 min, 10 min, 15 min --- times of each step. With occasional agitation. Plus final treatment in photo-flo in a separate tray.
1) I carefully shake off the reels with films and the tank (the lid is removed after fixing) to keep the amount of carried solution as small as possible.
I use this procedure already 2-3 years, and all my films are ok. Even though this time is not sufficient to experimentally prove the archival performance :)