m0useanswered grow question 2 years ago I would not unless it is needed, flushing soil can be complicated as it holds onto water more efficiently and can drown/compact the root zone much easier then coir or peat amended with petite.
Ask yourself why do you feel you need to flush? Flushing has been debunked for the most part and is only needed if you have been overfeeding and not allowing significant runoff. I would be monitoring the EC and PH of the solution going in and out of the pots to avoid the problem. fox farm nutrients feed heavy and they recommenced to flush a few times in their grow as this allows you to use more products and avoid some potential problems it would cause. Its a marketing game to sell more shit. If you have not been using a EC pen yet I suggest you prepare your feed to the ratios you desire then dilute it down to an adequate level to prevent build up.
If you still need to flush soil do it low and slow. Low rate of flushing over long periods of time. Not a massive bucket dumped in all at once. A weed sprayer with a few gallons should do the trick with multiple rounds. Best to do it outdoors or in a sink as there will be lots of runoff. following up with some microbes as they will be heavily stripped out of the medium is also a good idea. The golden rule for flushing is 3-5x the volume of the container. So if you have 3L container you want anywhere from 9-15L going though it.
Good Luck!