The erection drawing for this engine clearly shows a mud drum hanging like a uvula from the bottom of the boiler. Extending from this appendage, the drawing also shows a two-foot lever. This puzzled me for quite a while: surely you would have to unbolt the cover to gain access, and a lever wouldn’t be much help once the cover was unbolted.
I was getting ready to ignore it completely but then I learned that there is something called a mud drum plug, which is a blow-off cock screwed into the mud drum cover. I imagine if you are going to open the mud drum, it is helpful to blow as much mucky water out as possible before removing the cover.
As usual, one answer appears and raises two more questions. Would the mud drum plug have been operable from inside the cab? How should the shaft be supported? I’ve not yet managed to find a very good photo of a mud drum.