A cylinder-shaped sump, located beneath the boilers. The mud drum was meant to collect sediment from the boiler water. The sediment of raw river water settled in the mud drum and periodically was discharged overboard by opening a valve. The sound emitted when this valve is opened is a peculiar, hoarse, sullen roar, quite disturbing to passengers not acquainted with steamboats who frequently suspect the boilers are about to blow up. This procedure was called "blowing out the mud drums".