A few years back I saw a photo blog of a home build where they installed what looked to be a huge polyethylene water tank, something like
this. A guy climbed in the manhole and installed a big coil of copper tube, I think it was anchored with string.
The tank was placed in a small room not much bigger than the tank, just off the garage. After plumbing the connections, including a drain line out to the garage, they filled the entire room with blown cellulose.