I was at a hydro shop today talking about soil and coco in big pots, and the owner suggested to not water so much that you see runoff. He said it's best to water a 5-gallon soil pot with no more than 2-gal of water, because otherwise it could promote root rot from being too soggy at the bottom.
I asked him about cutting the soil with perlite, and he didn't recommend it, but made the above suggestion.
That gives me something to think about. When I was doing "soil," I would have ~30% (ballpark, varied) or more perlite. I didn't shoot for a mix that would be bone dry an hour after I watered, but I did try for something that was well-drained. Aside from not being "heavy" (we have heavy clay around here and I was looking for the opposite), my thinking was that there are air pockets in the mix... And that if I'd add a volume of water to a five-gallon bucket such that it would fill the majority of those pockets - and that if it was well-drained - that the action of the water draining out of the bottom of the bucket would pull fresh air into those pockets. Like when you draw out of a drink with your straw and then let go of it, the liquid drops and air enters.
Doing so seemed like a good idea. Not doing so
seems like a bad one. That doesn't mean that it is, but it doesn't come intuitively to me.
EDIT: To me, that wasn't flushing; flushing was using enough water (the 3x volume thing) that there was an actual flow into, through, and out while it was still going in.
And it (still) seems to me that root-rot (which I never had to deal with, so I'm just guessing, "I guess") comes not from adding perlite - which I'd think would help
prevent it - but, rather, in having a heavier mix that allowed the roots to stay wet. The word "soggy" comes to mind. The reason that a DWC doesn't get root-rot (well, done correctly, it
doesn't) is because you're saturating the liquid with DO. It's like it's not "wet" in the classic sense of the term.