I looked into the trenchless options, they don't really work for our scenario. First, the existing line might not be in good enough condition to support trenchless replacement. Also, while we can dig a whole at the city side, the lines terminate under the slab so there's no way easy way to create an entry point for the new line. There's also several joints under the slab, and we'd have to tear out the driveway to get to the existing line on one side. So far, our estimates are $12k (to tunnel to the two known breaks and replace only those portions) or $20k (to tunnel the entire width of the house and replace the entire system). A SEPARATE OPTION: I'm admittedly no expert, but I see a way to run two new lines - one up each exterior wall) which would serve the entire house with minor tunneling. The disadvantage is that the sewer line wouldn't be under the house, it would be buried under the strip of grass on either side. One company says they wouldn't do it that way because the line isn't protected by the house and could break more easily. To that, I say that if it breaks, it would be a MUCH easier fix than if a line were to break under the slab again. Is there any reason a new line can't be run outside the exterior walls of the house?

Thanks for the replies! I contacted my local wasterwater office, and the -- I believe it was our town engineer -- told the girl I spoke with, that "it's really hard to figure out". They didn't seem to know how to help beyond that. The girl in the office put me through to someone in charge of "building" & thought she may be able to help, so I left a voicemail and am waiting on a reply from her. I know there are companies that charge $ to find out where the lines are, but I'm hoping I can find out without having to spend money. Thanks again for the info!

Thanks, I did hire the job done. As I had the septic open he rotary cleaned form the septic end, which had a clog I misjudged. I took a garden hose and poked in the baffle/box and felt a solid bottom, thinking it was part of the concrete box. He said no and hit inside the box real hard with a pole and broke through. He did a little scraping with a pole scraper and asked me to run some water. Nothing much came through, so he took his rotary cleaner tool and ran it up toward the house from the septic end. That broke loose more "grease" and water began to flow. We then went inside as I had damaged the clean out plug and it was leaking through the center "Nut" area. He took a chisel and hammer and began to give it a real whacking, far more heavy hitting that I was prepared to do without specific experience, which I now have. He broke out the center and then collapsed the edge in.. then removed another couple of cups of grease and put on a new cap, using Teflon tape on the threads. Overall I see most, except the rotary cleaning, I could have done myself, oh yes, and knowing better how the box/baffle is constructed in the septic tank. I was surprised to see such a build up in the cast iron pipe, and I suppose even PVC does the same. Relative to using "Liquid Plumber" or whatever, the service guy noticed the smell of bleach/cleaner and commented. I confessed on what I had used and asked if that was a concern to him, he said he had no concerns. My concern, it didn't work or maybe even help.. a little help was no better than no help. I was pleased with the service and the charges seemed to be reasonable to me, and were flat rate, there was no clock watching. He was also willing to give me a little "class room" time so that I could do more myself.

you may not know but this pipe lining ws started over in europe the last 3 decades maybe 4? their infrustucture is way older than ours. where I am, it is all slab homes (no basements) mostly 1970's and 80ty's were made of cast iron. PVC started to make it way into the mainstream after that. These pipes are rotting away! when I say rotting I mean the base is gone.fractures are 1/2 inch and wider that are all over the place.sides,bottom, top, in lentghs that are in feet. Now you also have water lines in there.where? who knows. pipe bursting is not good because at every place a 2" or 4" pipe comes into the main line you have to dig up a section of floor to have a repair done et every interval. short of digging up the home and it had been done, pipe lining is the only real way to avoid a total rehab of the home. the co's that do this have a limited 50 year warranty on materials. it seals every joint,fracture all drains coming into the line and thats where they call reinstateting comes in. they have to open up all drains that where covered over by the material. so if europe started this,30 or 40 years ago and did all their streets (no digging up the streets all over europe) and I have not read anything bad happening I would not have any fears. like anything else,price and convience,where I am located sarasota fl this is the only way to fly! I am talking infustructure. if you had a cobblestone driveway the cost of lining would be cheaper than having someone come in to do the repair on top of the repair. also pipe pulling would in that case should be looked at too. BTW I also do this work