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At first glance that looked like a white frosted bulb with water stain on it. We don't use old painted iron pipe up here in the sticks so it didn't jump out to me.
Cast iron drain pipes were primarily used up until the 80s for their durability. They've been replaced with PVC since. Cheaper and easier to fix and work with.
Yes, there are old buildings in the city nearby that used to use iron pipe for steam heat registers, most got rid of the old asbestos snowman boiler and have converted to forced hot water (but retained the cast iron registers and pipe). Most everything built new is now pex, copper plenums, PVC drains, sometimes PVC supply lines.
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