Whenever possible, cut out the leaking joint and start over. A leaking solvent welded joint is an indication that the joint was not made correctly. It may not have been fully bottomed, a component may have been damaged or foreign materials may be trapped inside the joint. For a temporary repair, plastic fillet hot air welding can be used on the outside of the pipe and fitting to stop very minor leaks. This should only be used as a short term measure before the joint can be replaced.