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