Cisterns

I have photos but I can't figure out how to insert them...

I purchased a property with a 1920s fixer-upper house that has not been occupied for the last 10 years.  It's in a small town (population 338) in western central Texas.  It has city water and sewer and electricity now, but the original outhouse is still there and the pipe casing for the well is there, and there is a cistern.  The cistern is at least 10 feet deep, bell shaped, and unfortunately has trash in it.    

A poorly built addition was added to the side of the house in the 1980s I think, and for some unknown reason it was built partially over the cistern.  Once that addition was removed, I placed a piece of plywood over the opening to protect it, and keep me from falling in.  Later my handyman built the 'wishing well' to sit over the opening.  A few weeks later he placed stones around the base to help keep water from seeping in.

I want to use the cistern to hold rainwater runoff from the roof, so I'll need someone to clean it out, of course.  The water would then be used to water my gardens.  My question is, once the debris is cleaned out, I'm thinking I'll need to coat the bottom and lower 1-2 feet with something so as to seal it from contamination from the trash, yes??  Any suggestions as to what to use?

Here is a link explaining how to post pictures.

I hope someone with knowledge of your question will be along soon. Welcome to Permies!

Thanks Joylynn, I'll try to post the photos tonight.

This article from Penn State Extension may be useful. Rainwater Cisterns: Design, Construction, and Treatment. Welcome to Permies.

"This article from Penn State Extension may be useful. Rainwater Cisterns: Design, Construction, and Treatment."

Denise, thank you so much.  This article was very helpful!  I don't know if the cistern has a drain since it has so much trash in it, but I doubt it.  I believe it was built in the 1920s when the house was built.

To clean it out you could use a pulley system, with an automatic tipping system into a trailer.
That way it will be easy to get the job done and take it to a tip.
What diameter is the cistern?