If your Slave Driver likes to dump and run, start by documenting your own workload and that of your staff. Then note how the additional work overtaxes you, creating mistakes and causing delays.
Put the Slave Driver's work back on his chair. On top, place your analysis of the workload logjam and - while remaining positive and cooperative - ask to meet to review the work together to determine priorities.
Be constructive. Slave Drivers usually respond cooperatively when confronted with evidence that the work is excessive.
Don't be critical. With the Slave Driver's involvement, if possible, write up what is to be done first, second, and third and make sure he signs off on the revised priorities in case anybody asks how you arrived at them.