 Almost 100 years sometimes I've seen those date stamps in because this is the way manufacturers made these tanks. They always did that. Same thing with sinks, like kitchen sinks that are cast out of cast iron. I've seen the dates sort of actually cast right into those sinks. So that's one way to do it. Secondly is, of course, noticing what kind of building materials are being used here. For example, if it's copper plumbing, that's probably from the 60s.