It sounds like the other posts missed the point that it is at a joint. the smooth, stoneware looking sewer line was common until cast iron and then pvc. In your situation, u have a bell type fitting on one pipe and the other pipe joint slides into it. there were a couple of ways of sealing these, during original installation and they fell into two general catagories, rigid and flexible. It would LOT of digging to seperate the joint, so I would try patching. it probably has an asbestos type of gasket that has worn. Be sure the pipe doesn't flex at the joint, as the cause for wear and be sure to stabilize the joint, after the repair, (just create a hard, flat surface in the dirt and then stack brick or block up to the joint, finishing off with treated wood or whatever u need to "fit" the gap between ur homemade pier and the joint).
u can get any number of products, tar types, caulking tubes or pails. I would try maybe a combination. with the joint stable and cleaned, remove any loose joint material or dirt, grease or sewer residue. Use an underwater cement type of "puddy" and pack it in all of the way around the joint. small containers are available at big or small hardware stores. then, once it has cured according to label directions, go over that with a tar type of sealer.. as stated above, u can use a caulking guy type or a small bucket of it.
either way, use a putty knife to pack it into the edges between the pipe and the first sealer.
the underwater concrete will not be bothered by the existing leak, it will adhere to a damp surface and there is not enough pressure on a drain line to bother it.
after u have applied a good amount of the tar sealer/adhesive, wrap the whole area w/ tar paper. this will protect it from dirt and sharp rocks, for years and years, especially if u r filling the hole into the yard. watch it for afew days before u fill the big hole in and u should be fine.