Cistern use and drain

I found this metal cistern in a prime historic home yesterday. It is about 6’ diameter, about 20’ long of which 6’ extends into the basement and the rest is outside underground under the patio. It does not appear that there were any pipes on the far side for water inlet / outlet at the exterior, only the center and top holes at the facing side in the basement. Is that big hole a drain?! How in the world would it have been plugged? Imagine if it failed while the tank was full. I’d appreciate insights from those who have experience with these.

Interesting find Edwin, do you have any pictures from the exterior you could post?

I have zoomed in on your picture and it appears that it was designed to be closed by the rivets & metal. All of the water level staining lines up.
I have never seen a cistern with this type of configuration at the bottom of the tank before.

Thanks, I missed those you circled as possible original inlet or outlet ports. The outside portion of the cistern - about 70% of it - was underground with a patio over it, nothing visible. The mouth at the bottom is about 2’ diameter. Maybe it is a maintenance access port. I estimate the cistern as 6’x20’ for a volume of 565 cubic feet = 4230 gallons. My curiosity is how would that access port have been shut to keep 4000+ gallons of water sealed off. Any ideas?

1 Like

Maybe something inflatable?

Or this