This is how I flush...
First I wait until a plant looks like it's pretty close to done. Then I start thinking about how fucking much time I'm gonna waste trimming for days. Then I get lazy and say fuck it, I'm not going to mix up another reservoir, I'm just gonna give them water and deal with this shit on the weekend when I have time. Then I get interrupted 10 times and don't get to it over the weekend and I still don't have time to mix up a rez so I keep giving them water. Pretty soon the plants have turned all sorts of cool colors and I think, shit, I really gotta trim this crap before it goes to shit. So I give them another day of regular water and try and figure out what series I'm going to watch while I binge trim.
Flushing has an effect on taste however the 20 other things you fucked up and neglected while worrying about flushing have a much bigger effect.