'''When you are mating two different types of pipe you cannot reuse the gaskets or washers.'''.. you need new ones. There is a "goop" that you can put on threads to really seal them from leaking... also seals them from redoing the repair.
''I suggest taking a few pictures and the leaking ends of the pipe to your local hardware/building supply store and asking for their help/suggestions.'' The original "plumber" may have use poor or improper materials or left in cut/worn gaskets.
''If this answer is acceptable '''please remember to return and mark it'''.''