Well.... if you run 10 gallons of water through a 5 gallon pot you are going to be "flushing" way to many nutes out and we all know flushing is for toilets.
Right. I already did that on a past crop.
Dry these 3 gal pots hold eight cups of water. So I give it two more cups for the 10%+/- runoff. I don't let the pots sit in runoff. I dump the trays of runoff into a pitcher and that also verifies my 10% +/- runoff.
Speaking to your flood method.... With this transplant into new FFOF I dumped the 10% runoff from the trays into a pitcher then measured the EC. The EC was 3.5!
In the past I read on RIU to check runoff EC. In the past measured output EC was 3.5. Because I didn't know beginning EC was 3.5 I flooded the pots with gallons of water until output EC equaled input EC of my fertilizer, 1.5. I did that because I thought EC 3.5 was me over fertilizing, locking the plants out and the fert inputs were stacking. Nobody told me base FFOF has a 3.5 EC when new.
I was also led to believe "organic" soils/ferts wont measure an EC. "EC" only measures inorganic salts. Which clearly was bad info but I didn't know any better.
Thoughts on a scale? 1 cup of water weights about 1/2 LB. I can flood with 10 cups of solution, weigh runoff then generally know how much moisture content is inside the pot when I think it needs to be watered again.