Adding Fractions · Superchallenge problem

Some water is in a pitcher. Sam pours out an amount equal to $\dfrac{1}{4}$ of a full pitcher. Then he adds $\dfrac{1}{6}$ of a full pitcher. Then he pours out $\dfrac{1}{3}$ of a full pitcher. Now the pitcher is exactly $\dfrac{1}{3}$ full. How full was it at the start?