The current tank at Needleton gets flushed every fall right after the Silverton season ends, which I've done a couple of times. The amount of muck in the bottom is manageable with a fire pump to flush it out. I've been in the tank at Silver Plume and Dollywood, and I believe both were lined with a vinyl sheeting to prevent the wood from being exposed to excess moisture.
While the in-service tanks on the D&S aren't very attractive, they are a lot less maintenance. The biggest headache is keeping the delivery pipe from the reservoir and outflow at Tank Creek from freezing solid in the winter, and the Needleton tank to keep up with demand in the afternoon later in the season. At times, a fire pump has been used to assist the Needleton Tank by pulling water out of the Animas.
John Hillier