A sumpman was a specialized pitman's assistant tasked with keeping the lowest part of a mine shaft clear of water and debris. They maintained the heavy steam-driven pumping engines, pipes, and valves located in the engine shaft. The role required working in wet, dangerous conditions at the very bottom of the workings to prevent the mine from flooding.
Heard on the job
Send the sumpman down to check the intake valve, the water level is rising too fast in the main shaft.