I have a problem with a precast cistern that was installed in 1979 that seems to be plugged up. I removed all the dirt from the top and located the square opening to gain entry. It was about half full so I decided to be a brave soul and went in.
There was about one inch of really fine silt in the bottom and I could not find the output port anywhere along the bottom.
I am currently draining the system and hopefully when I get out all the water I may find it.
My question is, do most precast cisterns have a output port along the bottom edge?
And what would be the best formulation to disinfect the tank when the repairs, and all the silt removed is complete? I was thinking a mix of clorine and water on the way out.
I think the peoples kids I rented this property to for the last six years was the cause of the silt as I guess they used the check pipe to send stuff into the tank including some toy pieces.
Thanks to anyone who could help with this unusual problem.

speedball1

We don't have cisterns in my area but I did get some specs for a typical rainwater cistern. It has a 4" inlet at the top and a 1 1/4" foot valve with a 1 1/4" female threaded connection about 16" off the bottom in the end of the tank. Chorine and water would be a very good disinfectant. Good luck, Tom