Tunnel under concrete slab

I want to add a bathroom to a bonus room upstairs. My options for tying into the main drain in the slab are not good. Looks like the best thing is to run a drain down through the garage busting up the slab and then tunneling over to a closet that is 10ft away and then bust up the slab again. The main drain is underneath the closet. If I try to run the line through the attic I will not have enough slope on the line since it will be about a 35ft. run. Has anyone performed any tunneling like this before and can a DIY perform the task?

I would advise against tunneling under the slab. Cut the concrete, break it out and dig a ditch. Its safer, you are more likely to get the proper grade on the pipe and you can put the backfill in and pack it.

There are companies that specialize in cutting concrete. This would leave a much neater looking patch than if you just broke the concrete, and would be less likely to crack the driveway. I'm pretty sure it would be less expensive to cut the concrete, dig the trench, and patch the concrete than the tunnel method, and the tunnel would be virtually impossible to fill without leaving voids that would cause the driveway to settle/crack.

I would add - I have had various garage floor cuts and patches done several times before. If there is sufficient room to get a drill into opening, I have had the best long-term results by drilling holes on the edges of the opening sides so that you can pound in short lengths of reebar. These fingers of reebar stick out of the existing concrete. Then when the new concrete is poured to repair the opening, it gives the new concrete something to "hold" onto, rather than float.

A good concrete guy may have other tricks...