(sod the Whales Mode) - I'm not on a water meter, so I do my main rinse under a running tap for 5-10 minutes (as long as it takes to clear up the rest of the mess tbh...) Then - when that's finished, before I take the film out of the spiral - I just pour one pre-mixed measure of 300ml of water and 2 drops of ecover into the tank, swish it around a couple of times to ensure it's all been in contact (but as I said - i don't agitate it, or i'd end up with bubbles all over the film!) then pour it off and remove the film from the spiral. To be honest, I live in a area with pretty decent water quality, we're not badly troubled with kettles furring up etc so it's not particularly hard water. I know a friend had to use de-ionised water (from halfords - for topping up batteries iirc) for rinsing when he was at college as the tapwater was so poor.
I agree that the best way is to keep things simple - I did keep it simple - I simply opened the box of BnW developing kit a friend dropped off for me as he no longer used it, and in it were lots of little things like the film clips, thermometer, film canister opening tool... I'd certainly not have gone and bought them, but it seems churlish not to use 'em if you've been given them, doesn't it :shrug: