After about the 3or 4th round pull half, then if you want pull 3/4. Never more. You can let it sit like that until you are ready to add your tea again. Will take about a week. You can continue to drain 3/4. Make sure to stir well before pulling.
Not really worth the trouble. A gallon C/B you are only making 3/4 tea at the most at a time. That’s only after you well established brew. Start with one gallon, pulling 1/3 each round. So 12 cups sweet tea, 2cups strong starter and 5-6 oz scobie. Wait usually 14 days, start tasting 7 days.