How much water to feed my plants??

I'm pretty sure I've been overwatering my plants which has caused the unfortunate issue of fungus gnats. I typically split a gallon of water between two plants but have been reducing to about 1 gallon per 3 plants. I know this all depends on the size of the pot, soil and plant but I'm kind of just looking for a general, roundabout amount so I can be sure I don't overwater. Any input would be greatly appreciated.

well it seriously depends on your pot size. A gallon doesn't seem too much, but if we're dealing with party cups then it's kinda over kill. How big are the pots?

I've got 12" round pots, sorry I should have said that before. They're probably 3-5 gallons? I flushed them about a week and a half ago (right before I went into flower) and it took about 6 days for them to dry which concerned me. When you flush them how much water are you supposed to flush with?

^^^ 3 to 5 times what you'd water with

So then here's an example: 1 gallon of water/3 plants would equal 3 to 5 gallons/3 plants? Do I have that correct?