Plumbing: Sewer line my be damaged underneath house

I am on my 3rd plumber, and I think he is getting tired of coming over to my house. First one was too expensive, second one did not have a camera and after 3 visits gave up. The third one could not find my sewer line so he had to start at the cleanout a dig it up. He found that it went under an add on addition to my house. He replaced the sewer line from the cleanout to the addon addition and then from the addon to the street. He said it was clear under the house. Now it is two weeks later and the bathroom is starting to back up again. The only alternate route for the sewer line would be to break up my back porch that runs between my house and detached garage.
Is there anything that can be inserted into the sewer line under the house that will correct it. Somebody told my they thought that they had seen on the show This Old House sticking an inflatable sleeve in the sewer line and blowing it up to fix it. Has anyone heard of this and where can I find out more about it? I need some ideas.
The old pipe was a 4" clay pipe and they replaced it with PVC. The length under the house is probably about 25 feet and about 4 feet under ground.
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Aaron wrote:

Wait. He said, "it was clear under the house." Since he had it excavated right up to the house, presumably he could be quite certain it was clear under there. Eh?
So, what would be accomplished by "lining" the section under the house?
I'm not just trying to be smart here. Looking for more solid information so you can have some definite direction to go in.
How long have you lived there? The house must be about 50 years old, no? The add-on was done before you bought the house?
Just one bath? Does washing machine back up? Did this problem begin very suddenly? What else might have changed recently? Could the problem be that there is insufficient slope to the sewer line or that there is a belly/hump in the line?
Jim
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so has anyone run a camera thru the line? make a videotape of it while your at it.
our home has tree root troubles, with repeated clogs. so i dissolve rock salt in 25 pound bags perodically.
first you must find out why the line is clooging.
kids tossing debris down the toilet? tree roots? bad collapsed line crushed etc
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The house was moved to its current location in 1948. I am guessing the add on was done in the 60s.
the plumber did run a camera under the house and he said it was clear, but when he ran the camera the pipe was full of water so I am not sure how much he could tell.
The plumbing problem was caused by some foundation work done on the add-on part of the house. A pier was put to close to the pipe causing it to calapse. The plumber fixed that part. It has a been a nightmare because the foundation company did not know they hit the sewer line and the sewer did not back up until a month after the foundation work had been done. All the plumbers assumed that the sewer line went from the cleanout directly to the street. The 3rd plumber dug up the line and noticed it wrapped around the back of the house under the add-on section and attached to the city sewer on a side street since I live on a corner lot. This is when we found a pier going through the sewer line. This is my only bathroom and the kitchen and the washing machine attach to the pipe on the other side of the add-on so they are not backing up.
I guess the first thing I need to do is have the plumber run the camera again.
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Aaron wrote:

A nightmare, indeed!
Curious, that the line was full of water when he tried to run the camera. If we can assume that the line from add-on to the street was not clogged, this suggests that there is insufficient slope or there is a belly in the line. It doesn't take much of either to cause frequent clogging from TP, etc.
I have a suspicion that there isn't going to be an easy answer to this one.
Jim
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