So when flushing, Im yet to get a straight answer about this but, flushing is when you over water and let the excess water just run off. It helps to filter out the plant and correct ph by using correctly phd water. Yes???? And its advised to do between once a week and once a month and 2 weeks before you stop using nutes right???
Flushing gets rid of the built up salts in the soil and any nutes previously added. I usually do it every 3-4 waterings, depending on how the ladies are taking the nutes.

I wouldn't really use the word over water because that is what you do when you give your plants too much water over time (soil staying wet).

I flush 3 weeks prior to harvest. Two weeks of flushing then the last week for the "pre-drying" time(which means don't water the last week before harvest). Basically it aids in helping the plant dry a bit faster and break down the chlorophyll better.