It' supposed to fill the pores of the concrete and help prevent moisture from penetrating all the way through from the soil into your space.UGL Dry-Lok is one such product.

Also sandy, swampy soils, ew.

The hole didn't bother them (these were the tenants who were illegally renting rooms out to others so it's understandable why they would not want to report repair issues) as they continued to use the tub, rotting the floor underneath.

Now underneath that tile floor is one soggy mess including mold.

Soil is mostly clay which causes settling if foundations are not frequently watered.

Would there be any chance in next 30 years that someone mandate the soil test even though there is no more tank left?

Even if the inspector verifies that there is no leak I was still hoping to sample the soil and have it tested at a lab for my own piece of mind.

Hi @Mary Meyer, most contractors in my area will install a base (the depth of which will be determined by the condition/type of soil at the proposed site, usually 8"-12") of very well compacted 3/4" or 1/2" gravel which is blended with smaller aggregates all the way down to a sand-like size. 

Here is a photo:I'm in for the long haul...I want the floor underneath!

Half the time these are built on dirt with no crawl or access underneath.