My house is just over 10 years old and recently water started backing up into the 2nd bathroom. Two plumbing companies ran cameras and found two bellies: one at 15' and one at 30' - they are under the foundation. A foundation guy came out and quoted me $400 per foot and at least 19' and couldn't guarantee it wouldn't be 40'. Homeowners insurance doesn't cover this work and neither will the builder though the builder says that a beam that runs the length of the house could have caused these bellies. I am lost on how to handle this.

There is no way around this issue, the main has to be relayed. Its going to be expensive and no one else is going to accept responsibility including insurance, as you have found. Get at least 3 bids quoting the same work. If the belly is under the foundation the job will likely call for excavation inside the home and outside.

Any plumber suggest the possibility of rerouting the drain around the foundation instead of under it?

You could try suing the builder, if you bought it directly from him when new. You can use Small Claims up to the maximum in your state, even if the work cost more. But such things may be seen by the courts as expected problems over time. And bellies happen when not under foundations too.

Joy, think you may be picturing this wrong. Sewage is created inside the home , so inside the foundation. It has to exit somewhere. Got to go through or under the footing to get outside.

@joypulv & ballengerb1 Thank you. The foundation guy said that he is going to approach it from outside instead of messing with the inside of the house. No one has suggested rerouting the drain though it does seem like it might be a cheaper? Option. I've had the house since new. Its like my worst nightmare.

I thought this went for 30-40 feet under the slab?
Mine goes 25 feet, and I could change it to 4' if I needed to.