: 1) Tunneling under slab and replacement of cast iron waster water system with PVC.

: 2) Also installed 3 two ways clean outs and repaired two water leaks.

: This was for a total of $18,000.

: Our problem is this. About every 3-4 months, our bathtub drain began to slow down. Then the toilet drain next to it began to shows sign that it too is slowing down and began to clog and overflow. When it does, the waste from the toilet would some how flow into the bathtub drain hole and into the tub. It is a disgusting site. We have tried liquid plumbing and none of it seems to work.

: From the work done above, can any of you experts tell me exactly:
: 1) What was done under the slab?
: 2) Is it normally for toilet drain to backup into the bathtub?
: 3) Is it possible that the work was not done correctly and causes this problem that we are having?

Tunnelling usually does not provide the access to replace the drainage system. When the toilet backs up into the tub drain it indicates that the main sewer line is clogged and needs to be cleaned. You need a machine. Liquids seldom work. If you are having it cleaned every three months then something needs to be done and a camera is a good source of information.j
Your jurisdiction's inspection department should have records on what work was done that required a permit.
LonnythePlumber