As part of our basement remodel we will be replacing our oil furnace with a gas furnace.  I would love to be able to reuse our underground heating oil tank as a rainwater cistern.  I would use the collected water in the yard/garden during the summer.

Normal decomissioning of a tank (if left in place and not filled with foam or concrete) is to "triple rinse" it, through the fill tube.  This would obviously not be sufficient decontamination for my purpose.

I am thinking that we would need to cut into the top of the tank and get someone inside it to scrub it down thoroughly with detergent, to get all residue out.  If this is insufficient, perhaps an epoxy coating. 

The various local oil tank decomissioning contractors I have spoken with are not up for this project.  Too weird for them.

Does anyone have any words of encouragement/discouragment as to the practicality of this project, and how to find someone to do the work?

Thanks!