I designed a city water tank like one near my home. It is in n scale, but easily rescaled in your 3D printer software. It is a .stl file. It is open for download. Please, no commercial use per TinkerCad rules.
https://www.tinkercad.com/things/hwuvzHrWoAK-city-water-tank9/14/2024 I revised the design to add a base plate. This stabilizes the piping. Same URL. Have fun!