My house was built in 1915 and in the back yard there is a partial tank that I am not sure what it is or what to do with it. There is a brick well/cistern with hand pump closer to the house (2ft diameter) however this is about 25-30 feet away. I first discovered it after buying the home and it looked like a metal ring roughly 8-9 feet in diameter. So of course I started digging and found it had metal walls, estimating that it is 4-5ft deep (have not finished digging). While it collects and holds water after a rain, it isn't fully water tight as the water drains after a week. Any thoughts on what it is or what to do with it? Water seeps in so a small pond, fountain, or even planting doesn't work. Thanks for your help.