any science you can find will tell you flushing is bullshit. ask any farmer that grows any kind of food crop, that grows tobacco, that grows anything, they'll tell you the whole concept is wrong and does nothing but deprive your plants of nutrients. you CANNOT remove nutrients from a plant with water. period. cannot. not with the whole ocean and a funnel. what you're doing is leeching your medium. that starves your plant. thats not a good thing.
its actually hard to find any info on this practice, because no one else in the entire world uses it, because its ridiculous, a waste of time, and potentially harmful to your plants.
i can't believe people are still doing this. and spending money on useless products....you're trying to remove stuff from your plant, so you add more stuff.....makes as much sense as the whole concept to begin with