I'd like to bury a cistern to collect water from my gutters. i have some rain barrels already but for this particular application, I need something bigger and something that can be buried.

I've seen some plastic water storage tanks but they are too tall. I was looking for something a little flatter but wider so I could bury.

Any idea who might have a selection of such things? I've searched the internet but no luck so far finding anything.

thanks!