Whenever I flush in fabric containers they never se to drain right and they remain heavy for a long time. I'm experimenting with punched holes in the bottom to see if it helps drainage problems with fabric pots. I've always went by the size of the container. If using a 3 gallon container, flush with 3 gallons of water. If using a 5 gal....and so on. It's always worked for me when I used to make the occasional fuckup and plants were pretty fast to recover. I like to flush the week before harvest to rid the soil of any leftover nutes but those fabric pots aren't the best for draining large amounts of water. Some people use a flushing agent also, but I find ph'd water works well enough. It also helps if your soil mix drains well too. I use 1/2 FFOF 1/4 perlite and 1/4- black cinder. No more drainage problems anymore. Good luck!
View attachment 3653845