I have bought a house where the current owner has recently converted the old cistern into a "septic system". I understand he pumps it out every 3-4 mo. Once settled, I would like to return the cistern to a water catchment system for yard/garden use only.

First- Anyone have any thoughts about using an old cistern in this way?
Second- I am looking for suggestions as how best to approach cleaning/sanitizing the tank, etc?

I've never had a cistern before but I understand how they work, etc. Your help is much appreciated.