Chicago might require cast iron, so check that first. Otherwise, underground, you can use a Fernco fitting. This is essentially a thick rubber sleeve with screw clamps at each end. It requires that you torque them properly and backfill and support the line properly, but are approved for use underground. What caused it to sag? Make sure when you replace, you don't end up with the same problem!
Another possibility if you can remove the pipe from a hub, is to use a Fernco donut. This is inserted, then the PVC is pushed inside. The rubber compression makes the seal. Sizing these for proper fit is critical. This might take care of one end, and the sleeve on the other. Just depends on what you have, and where it is.