I don't know the answers to all your good questions but I can offer some information about the Osier and Chama tanks. Osier's tank was rebuilt last year and I believe was painted the same color as the Section House and Station building which is a dark reddish-brown. That color at Osier was chosen to represent a certain historical period of the railroad during the early 1900's just like Sublette colors are painted to represent the pre-abandonment period (pre-1970).
The Chama tank was completely rebuilt during the mid-1990's. There was an excellent article in the C&TS Dispatch several years ago which covered the rebuild. The article contained a great amount of detail. Maybe another reader remembers the exact date of the article and could post a date. I saved it but could not locate it.
As far as the remainder of the water systems, I was told the railroad operator itself maintains those. It would be interesting to find out if the water plugs at Sublette and Cumbres have valves that shut off the gravity flow of water to the plugs. One would think the water plug itself would freeze up and bust since they are exposed. I wouldn't think a cystern (sp?) reservoir itself needs maintanance beyond periodic checking for debris.
I learned from this post that the Lava Pumphouse is in not-so-good shape as far as the internal workings go, but not hopeless. This may already be on the Friends long-term project list? I find it interesting that the Lava pumphouse is still there and could be restored. I also understand from prior posts that the pumphouse engine is safely removed and on loan to a local museum (politically correct someone?).