What was found
(CAN) DURING TAXI FROM COMPANY RAMP THE LAVATORY SMOKE DETECTOR INDICATOR ILLUMINATED, VISIBLE SMOKE WAS OBSERVED IN THE CABIN. THE AIRCRAFT WAS RETURNED TO THE COMPANY RAMP AND SHUTDOWN. MAINTENANCE FOUND OIL DRIPPING FROM THE NR 2 ENGINE TAIL PIPE. IT WAS DETERMINED THAT A COUPLING HOSE IN THE ENGINE VENT LINE HAD FOULED DURING REASSEMBLY. THE INNER LINING OF THE COUPLING HAD CAUGHT ON THE TUBE FOLDING INWARD CAUSING A BLOCKAGE IN THE VENT LINE. THE COUPLING WAS REPLACED AND THE AIRCRAFT GROUND RUN AND TEST FLOWN BEFORE RETURNING TO SERVICE.