If you are using just clean Ph adjusted water it will take about 14 days to do a proper flush.

You don't need to over water them to do a proper flush, drowning your plant will not help to flush them any faster. The plant need to uptake the water too so you can clean out the inside of the plant as well and not just the soil.

Using a commercial flushing product is always a bonus and can speed up the flushing process by a week.