What was found
AIRCRAFT WAS GROUNDED: SOF EVENT OCCURRED DURING TAXI OUT, SEVERAL MINUTES AFTER ENGINE START. IDENTIFIED VIA AFT GALLEY FLIGHT ATTENDANT, (DIRTY SOCK, ELECTRICAL ODOR). STRONGEST ODOR IN AFT RIGHT GALLEY GASPER. NO OTHER AIRCRAFT JET ENGINE EXHAUST IN VICINITY, NO TAIL WINDS. REMOVED AND REPLACED AFT SILL DRAIN VALVE, PER JC 09C10038005. OPERTIONAL CHECKED GOOD.