You could be stepping in it, literally, if you mess with a sight glass on a pressure tank like columnist John Schmitt did. Source: iStock
One thing that was quite common back in the day and that we don’t see at all anymore, at least in smaller tanks, is a sight glass. This was a small glass hollow tube that ran up the side of the tank. They were usually installed about two-thirds of the way from the bottom to the top. The tanks would have tappings, usually -inch IPS, where special fittings that accepted the sight glass could be installed. As I remember, these tappings were about 18 to 24 inches apart. The glass itself was maybe -inch outside diameter, and it was protected on the outside by two brass rods so it couldn’t easily be broken by being bumped.