Leak in sanitary, how to proceed?

[DDOntario]

Hello,

First time post, long time visitor to the forum, helped me out many times - #1 plumbing resource for me.

I have a leak in my sanitary line and access is limited.

Preface
My home is on concrete slab with a main, in-grade 3" cast iron sanitary line .
One full bath and kitchen feed into it, no plumbing issues or blockages.
In the basement, the 3" in block coupled to a 4" cast iron leads thru and out to the adjacent wall to the exterior.

Problem
Sewer water coming up from floor at hot water tank pedestal

A drainage company completed camera inspection found normal conditions - water in pipe, no intrusion or obvious breaks - inconclusive. His best guess is that pinholes developed in the 3" cast iron at the block wall and it leaking down and finding it's way thru the floor. His advice was to 1) remove the hot water tank 2) break wall area around the pipe to work, cut the 3" flush at the wall and sleeve a 4" ABS with a coupling over the 3" tighten and connect 4" ABS to the remaining line out. A family friend, veteran of 40+ of foundation work agreed, no other alternative. Both gave me the same look - roll up my sleeves and go at it - not many local companies will want to tackle the job.

I consider myself a handy homeowner, but this is something I've never done and I fear what lies behind the wall. I anticipate it being a smelly. messy job. Trying to visualize the steps - flush the pipe and clear out best I can, cut, lots of rags, buckets, and hope the 3" integrity is good enough to tighten the coupling.

Anyways, any input re: the proposed fix is appreciated along with any tips you might have.
Thanks in advance

 

[Reach4]

My home is on concrete slab with a main, in-grade 3" cast iron sanitary line .
One full bath and kitchen feed into it, no plumbing issues or blockages.
In the basement, the 3" in block coupled to a 4" cast iron leads thru and out to the adjacent wall to the exterior.

I think you are saying that the line to the city sewer goes through the basement wall.

Why doesn't the salesman think that this is not a case of ground water coming in at the basement floor?

Problem
Sewer water coming up from floor at how water tank pedestal

Could you clarify that? What is a water tank pedestal?

 

[Sponsor]

 

[DDOntario]

I think you are saying that the line to the city sewer goes through the basement wall.

Why doesn't the salesman think that this is not a case of ground water coming in at the basement floor?


Could you clarify that? What is a water tank pedestal?

Correct - line to the city sewer goes through the basement wall

Why doesn't the salesman think that this is not a case of ground water coming in at the basement floor?
Due to the smell and water comes up only after bath or kitchen are used

What is a water tank pedestal?
The 2" pad the hot water tank is on, it's what he called it haha.

 

[Reach4]

Problem
Sewer water coming up from floor at how water tank pedestal

Why doesn't the salesman think that this is not a case of ground water coming in at the basement floor?
Due to the smell and water comes up only after bath or kitchen are used

That is a good reason.

Why do you think the problem doesn't continue 2 ft or 50 ft into the yard?

 

[DDOntario]

That is a good reason.

Why do you think the problem doesn't continue 2 ft or 50 ft into the yard?

That's the unknown.
Drainage guy said to try the fix at the wall, high probability that's where it would be.
If it doesn't work, then that would eliminate one variable.
He said it's unlikely its anywhere else and no indication from the video

 

[Reach4]

indication from the video

Ah, there is a video of the upstream pipe.