Oren wrote:
Discovered today from my plumber. I was stunned. My mind, and my
bride's mind is spinning where to start for recovery of bad plumbing.
It has to be fixed. regardless.

Single story, concrete foundation. Parts are missing from drain
plumbing so water drains directly to soil under the foundation
(cooties).

House it 20 years old, I bought as second owner.

The rubber gasket and tub shoe is not present so water drains directly
to ground soil. The tub has a "tub basket", even has plumbers putty
on it. Just pull the drain out, look and water under the tub. I was
stunned.

Sample pic:

https://tinyurl.com/y7n9dche

Were would you start to rectify the problem.

I'd start with a camera inspection and see what's what and where issues
exist, then see if it's possible to bust out slab to fix in those areas. How
did this ever pass city inspection when house was built? I'd avoid
"tunneling" under, as its been my experience it's unlikely to get all soil
compacted back in. YMMV