Hello - we have a condo in Florida that has been sitting vacant for the last year. It is not that old, about nine years. Recently we had the water treatment media replaced and when they flushed the lines, water started leaking into the living room through an air return vent. A plumber opened up the ceiling and found the leak - it looks as though the PVC drain pipe failed in the middle of a wye joint (picture attached). Any idea why this would have happened?