I also flush with straight water(PHed) twice, once at the beginning of bloom and once at the end. Personally, I don't use 3X the pots volume, it's closer to 2X. BUT, I have to down to a science, monitoring runoff until I KNOW it's clean, then stop there. The key is to pour the water in evenly, so the soil gets cleaned evenly. I use a watering can with a sprinkler type head, which simulates rain, and washes the soil nice and evenly. If I just dump a bunch of water in really fast, alot of it runs down the edges of the pot, finds channels to run through quickly, and doesn't flush nearly as well as if you do it carefully, and evenly. IDK about you, but I'd much rather pour in 10 gallons per pot, than 15 gallons.