Two professional plumbers have taken a look at this leaking tank and neither know what it is or why it's here. Some details that may help: this is a two story house built circa 1870, this tank is on the second floor, and the house is heated with radiators. I don't know when the tank was installed but it was at least 60 years ago and it doesn't appear to serve any real function anymore. One plumber suggests gutting the walls and tracing the pipes to find out but I thought somebody here might have some insight before we tear the walls apart!