Bruce I have operated mine with as little as 90 gallons of sap. I had permeate saved up from previous use to clean it with though. 300 gallons will give me enough permeate to clean the RO with. I like to have a lot of sap so that I can get it real sweet, 16% to 18% so that I don't use much wood and draw off a lot of syrup in a short time.