As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
STRONG ODOR COMING FROM THE BACK GALLEY. REMOVED FROM SERVICE. VERIFIED ODOR NOT TO BE FUEL, OR OIL, OR HYDRAULIC FLUID. ODOR WAS COMING FROM AFT WASH BASIN DRAIN TANK. EMPTY THE DRAIN TANK, AND ODOR WENT AWAY. NO OTHER DEFECTS. RETURNED TO SERVICE.