What was found
AIRCRAFT 9872, ON LEFT, SINGLE ENGINE TAXI WITH THE APU ON, THE AFT FLIGHT ATTENDANT REPORTED SMOKE IN THE CABIN AT GATE. CREW SHUTDOWN PACKS AND APU AND, PER QUICK REFERENCE HANDBOOK, PASSENGERS WERE DEPLANED. LINE MAINTENANCE RAN APU FOR 20 MINUTES, THEN INSPECTED APU FOR OIL LEAKS. NO LEAKS WERE FOUND. DUE TO LARGE AMOUNT OF OIL IN APU ENCLOSURE, APU WAS REPLACED PER AMM. LEAK CHECK GOOD. AIR AND ELECTRICAL OPERATIONS ARE NORMAL. COMPLIED WITH SMOKE IN CABIN TROUBLESHOOTING. ACCOMPLISHED PACK BURNOUT PER AMM. REPLACED COALESCER BAGS PER AMM. AIRCRAFT OK FOR SERVICE.