Hi Jim:
The octagonal structure in the photos may or may not be a water tank, but is definitly not a railroad structure.
The C&S employed the use of two round 50,000 gallon water tanks at Como, one immediately behind the stone part of the roundhouse, the other was down at the South end of the yard. Both were removed ages ago.
After abandonment, Cooley Brothers construction occupied the railroad facilities and made several changes. These included removal of the stone boilerhouse to allow access by their trucks into the roundhouse from the town side. If the main part of the building in the photo was in fact a railroad structure, the octagonal addition was added after the C&S was long gone.
Thanks, Todd for posting the turntable information.