As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED. LHR, AIR INTERRUPT, FCO-ORD. EMERGENCY DECLARED. LANDING UNEVENTFUL. AIRCRAFT OVERWEIGHT. DURING CRUISE THE 4L AND 4R LAVATORY SINKS FILLED THEN OVERFLOWED WITH WASTE WATER. REMOVED AND REPLACED DRAIN MAST GRAY WATER RESTRICTOR VALVE IAW AMM 38-31-02. OPERATIONAL CHECK NORMAL.