Well, my outdoor Asian Haze would drink three gallons of water in less than 36 hours
I suggest that you fully water your 5 gallon pot to get a starting point. You'll have a muscle memory of her weight to tell you when the water.
You should have a rough idea of how much water you're gonna use in one setting. Take half of that and slowly water with a sprayer, preferably with some sort of Surfactant in it. let it soak in thoroughly. Then take the remaining water and bottom water. Same as before, do it in cycles with time in between. You'll see how quickly the pot takes up the water. when the pot doesn't take up all the water within 10 minutes, the pot is fully watered. Pick the pot up and remember the weight. You can drain the water out of the tray once it's to that point. The next time you do it, you'll be able to pick up the pot to detect the weight and you won't have to drain the tray at the end.
That way you're doing it consistently and can realistically judge water usage.
Bear in mind that procedure is for a organic grow. If you're using salts you can run into accumulation problems . I never had a problem with it, but I was using mega crop at a low dosage every watering.