As a general solution for this type of puzzle, with two pails:
Label one pail A, and the other B.
Fill up pail A. (point 1) Empty pail A into pail B until either A is empty of B is full. If B is full, empty B. Check how much water is in A and B; see if the answer has been reached. If the answer has been reached, stop. Otherwise, if A is empty, refill A. Go back to (point 1) and continue from there.