If you have a leaking underground PVC pipe, there are a few things you can do to fix it. First, try to locate the leak. If the leak is small, you may be able to repair it with a PVC patch kit. If the leak is larger, you may need to replace the section of pipe that is leaking. To do this, dig up the leaking pipe and cut out the damaged section. Then, install a new section of pipe using PVC couplings and primer/cement.