I used fresh water yesterday.
However, I'm not sure flushing is any more than a word, anyway. This plant and this soil has has nutes for 6 months. It's entire life. The soil, the roots, and the plant, itself probably have an incredible build up of nutes.
I'll bet (just guessing here) that if you could measure PPM of soil and of the plant, itself, one might find that a few days (or even a week) of flushing makes little or no difference.
Might be a nice experiment.
I must admit, it has always been my policy to lighten up on nutes at the end but that is because I usually have them so pumped up by then, that the nute burn is setting in and they really need a little break anyway.
I am getting ready to flower a handful of clones of these so when I harvest, I'll flush half and not the other. Guess that's one way to tell.
Either way, that is always a controversial topic among growers.