Hi WildBill. Sorry I missed your post/question back on Mar 7th. Me bad.
I'm a huge fan of Rain Science Bags. I have been using them since introduced here in a product-review grow test back in January 2019. I was one of the testers. Its now the only thing I use except for two 2-Pot AutoPot systems. I've used them with different nutrient programs, both with success. I tend to load them with a mix of coco and soil. I like to keep the mix fairly "fluffy" in terms of not retaining too much moisture. My gold-standard is the 3-gallon bag. I do have a few 5 gallon bags, and four 10 gallon bags that I used last summer for an outdoor grow. But 3-gallon is my go-to.
They do dry out real fast when growing outside, but I only tried outside once, and don't plan to do it again anytime soon.
My watering/feeding strategy is to get about a pint or so of runoff. So, yep, I always water until I get runoff out the bottom. For me this is easy to see and measure because the bags sit on rolling trays that have a removable runoff capture tray underneath. I also cut out a circular piece of rubber floor mat (kitchen/garage) that has holes in it. The mat sits in the tray and gives the RS bag even more circulation and an easy way to expell excess water without siting in wet standing water.
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The exception to this strategy (of getting runoff) is in the early days when a plant is still tiny and has not developed a full set of roots. I'll water/feed then just to get a modest amount of moiture into the bag. I'll often use a little moisture meter to help me know when & how much to give. Once the plants leaves have extended beyond the sides of the bag (about 3 weeks or so) then I'll starting increasing the water to get the runoff.
Frequency of watering really depends, obviously, on the size of the plant. Early on I can go 3+ days between watering, and 2 liters/quarts is sufficient. In full maturing flowering mode its usually once every two days. Occasionally I have a beast that demands 3 liters/quarts, and/or daily feeding.
To ease the time spent doing manual feeding on such a fequent basis I am considering adapting a couple of RS bags for bottom feeding using some equipment from AutoPot. Haven't pulled the trigger get on the $$ investment, but probably will in the near future.
Hope this helps, Any questions?