It seems that most of the pipes that are talked about on this site that has problems are metal of some sort, and they haven't lasted 100 years. I personally would choose any option but that. Have you checked into the siphon drain system I mentioned? By your description of a 48" stand pipe, it sounds like the drain is at the bottom of the dam. Thats trouble if it ever has to be replaced and is more likely to seep.
