Interesting approach. 3.5 gave me this as its second answer:

1. Fill the 6 liter jug to its maximum capacity. 2. Pour the contents of the 6 liter jug into the 12 liter jug, which will leave 6 liters in the 6 liter jug. 3. You have now measured out exactly 6 liters of water using the 6 liter jug.