As it was mentioned to always end on a flush aimed at a PH of 6... that's what i don't do.
When i flush, i don't care about the PH level anymore, but use tap-water (unless you're flushing with a diluted nutrient solution), and here's why:
The reason for getting the proper PH levels during regular growth are so nutrients can properly be taken up by the plant from the growing medium.. when we flush, we want to get rid of the nutrients inside the growing medium, and want the plant to use up what it's already got inside, so why bother adjusting the PH, so it can take up even more from the left-overs from the flush (that might not be metabolized in time)?
If anything, in theory it'd make more sense to change the PH to a value that doesn't kill the plant, but hinders nutrient-uptake from the medium as much as possible.
Again, one of those topics where there are many different opinions ;)
In either way, happy growing!