Small pinhole leaks in PVC piping normally occur in the connections between the PVC pipe and a PVC fitting, where the connection has not sealed correctly. To repair a pinhole leak, you need to use a material that bonds to the PVC pipe and creates a permanent repair. There are products, similar to epoxy, that are designed specifically for PVC pipe repair. You can use these products to seal pinhole leaks around PVC connections and pinhole leaks in the PVC pipe.
Turn off the water to the PVC line that has the small pinhole leak.
Use the 200-grit sandpaper to remove the shiny finish from the area around the small pinhole leak.
Wipe the area around the leak with a clean rag to remove dirt and debris from the surface of the PVC pipe. You need to make sure that the area around the leak is completely dry before you proceed to the next step.
Mix enough liquid repair plastic to cover an area the size of a quarter.
Dip the two-inch paintbrush into the mixed liquid repair plastic and brush the mixture onto the area of the small pinhole leak.
Allow the liquid repair plastic to cure for the time specified by the product's instructions before you turn on the water to the PVC pipe.
Inspect the repaired area of the PVC pipe to ensure that the leak is fixed. If you notice water leaking from the area, repeat the process and apply an additional coating of liquid repair plastic to the problem area.