OK, here's the plan. I washed out 2 1-litre jars. I will measure out 1200 mls of water (straight from the hot water tap, btw) and then pour 300 mls of water in the two jars. I will then stir up the 2 jars of fermenting liquid (called "wort", pronounced "wert", I believe) and pour 300 mls of wort into each of the two jars of water, and then pour 300 mls of water into each of the two jars of wort, now having 300 mls left each. Woo-hoo. And you thought I couldn't do the calculations.