So, I've been doing the Ilford method for years (or a modification of it - in total, 9 to 10 water changes). I think I use about 5 to 6 litres of water to wash a roll of 120.
The main reason I use this method is the water temperature in my laundry is too variable. This morning (Australian winter), the water was coming out at 14 deg C. In the dead of summer, its not uncommon to see what coming out at 26 deg C.
But doing this wash method can become a bit of a drag if you have a full day processing in front of you. So, I've been thinking of building a tank with a small pump to do the final wash.
If I read the Kodak literature for film processing, they suggest washing for 20 to 30 minutes, with a flow rate that changes water every 5 minutes. So, If I wash in a 1 litre tank (which I typically would), I am assuming I'd still get away with less than 10L to was a film and a flow rate of around 200ml a minute.
Does this sound like a daft idea?
The idea of a watertank isn't a daft idea at all!
AAMOF, I do the same, till a certain extend, I have a few jugs of 5L standing overnight to acclimatise to room temperature (+/- 20°C) during the winter, and immerse some frozen ice accu's in the summer.
I have stainless steel tanks for one, two and four 120 reels, the middel one is used the most and contains 800cc (they all have 400cc per roll).
There is an electric 80L water heater in my darkroom, but that's a bit of overkill for just a few tanks of roll films, and in the summer a heater isn't that useful as my darkroom is on the top of the building just under the flat roof causing the room temperature to rise till 32°C (regardless the 14cm insulation), and the tap water is around 25°C (and an air conditioner is a too greedy energy eater)...
I do the Ilford method (for FB paper too) but add an Adox Adostab bath at the end which contents some Agepon too.
BTW, water is too precious to waste, and energy (and life) is getting more expensive by the day thanks to Vladimir P., that's why I hold a bit on analogue photography...