As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER TAKEOFF AND LEFT PACK TURNED ON, CAUSTIC FUMES FILLED COCKPIT. DECLARED EMERGENCY. RAN FUMES EVAC CHECKLIST WHILE RETURNING TO LAND . AIR TURN BACK. R & R LEFT WATER SEPARATOR SOCK, INSPECTED R-SOCK FOUND NO DEFECTS. LEFT SOCK FUEL FUME SOAKED.