Some extra details about watering two liters.
24 hours after I feed, the water in the rez is mostly drank up. For the next day its the water in the vermiculite that the plants are using.
This current run my drain hole in the hempy two liter is 2 inches up from ground level.
For this next run I made the buckets with a 2 and 1/4 inch rez in anticipation of going a bit bigger.
Also if you think about it, the bottom of the two liter is stealing some of your volume. The molded plastic feet that are 1/2 up and 1/2 down take away about quarter of your total rez capacity.