Flush products really breakdown the chemicals so that water can remove any residuals and chemicals that have built up in the medium/plant foliage. If however you are using weak organic fertilizers, then you may not need to actually use any kind of "Flush" product.
Although if you are using hardcore chemical fertz. to get the most from your yield then you will definately need to use a flushing agent. I read a lot of people saying it is too hard to match the vol. of pots with the same vol. in flushing solution. Yet it really is mega easy. You simply pump (Maxijet 1500) the drained liquid out down a hose to whatever outlet you desire, i.e. toilet bow; sink; outside drain etc. (Make sure to bleach after if outside drain for certain smells might get you in trouble.)
The more powerful your pump the faster the task is! It is so so worth it I cannot stress enough after the heavy flush, leave for 36 hours. Then I feed with clean "Flush" liquid on normal feed plan for another 4-5days. Then after that I flush with normal water at rate of pot vol so 11lt pot gets 11 lt water. then pump that back out and stop feeding plants and just leave them for 48 hours with no tubes attached so that they semi dry up a little. (They will have a very wet clean medium anyway so will do no harm.) This will make the dry-cure time faster. Especially if you use sillica gel packs... 2kg of sillica removes 1 3rd of 2kg in moiture from harvest.
I also use bubble pots too they are mega easy to flush you just empty nute solution then fill up with flush solution leave it to do its thing topping it up whenever needed. Then after 5 days just empty replace with clean fresh water and then after 2-5 more days (depending on size of plant,) of normal bubble pot behaviour I drain and leave for 24 hours, job done.
The flavour will be so so amazing well worth the extra effort. Oh and I use
advanced nutes ph balanced A/B brands for the ease of use. Along with their amazing "Overdrive" product and Canna Flush for the flushing solution.