When you flush you use enough water to fill the pot and let it drain out altogether. It is a one time thing, once you flush you let the plant go without watering until it needs it again. I suggest a moisture meter, picked one up a Lowe's for five dollars. If your soil has nutes in it already, a proper flush is needed to get the nutrients to start working. Flushing is good every once in awhile to get rid of sodium buildup in the soil. Hope this helps, peace.
thanks for answering another ques i had via another post. thanks man. this guys contribution is well appreciated by myself.There are a few reasons to flush...one to correct a problem and two to clear out all the nutrients in the soil before harvest. If your flusing, you should use 3x the amount of water compared to the size of the container. Make sure you have good drainage and it really dont matter how much water you run through it.