Here’s a trick that I’ve used to fix a leaking joint in a PVC water-supply line. As shown in the drawing, I begin by cutting a coupling in half, making sure that I’ve removed the stop in the middle. Next, I cut one of the coupling halves in two. The ratio should be roughly 60% to 40%, with the larger piece just big enough to not break as it is pushed onto the pipe like a C-clip.
I shut off the water and drain the line to stop the leak, and let the joint dry out completely. Then I apply glue to both the pipe joint and the patch. For this, I use multi-purpose glue made for both ABS and PVC pipe because its thicker consistency works well in this application.
With the factory-edge side of the modified coupling toward the leak, I snap the patch over the pipe and slide it hard against the leaking joint. There should be some glue squeezing out of the joint. I let this dry overnight, and by morning, the water line is ready for use.
Bruce Calderwood, via email