What was found
AFTER TAKEOFF, AFT LAV SMOKE DETECTORS STARTED SIGNALING WITH SOME HAZE IN THE CABIN. RETURNED TO CVG. PERFORMED DUCT BURNOUT PER M/M CH 36. CHANGED WATER BAGS, RAN BOTH ENGS TO TAKEOFF AND NO SMOKE OR HAZE NOTED. ENGS STARTED WITH EXT AIR. APU NOT USED. REPLACED APU AND CLEANED DOORS, RAN APU AND NO LEAKS. ALL INDICATIONS NORMAL. RAN SEVERAL HRS, NO SMOKE OR HAZE.