As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FORWARD LAV TOTALLY OVERFLOWED AND COULDNT MAKE IT STOP UNTIL SYSTEM DEPLETED WITH SELECTOR OFF IN ALL POSITIONS GREY WATER THROUGH OUT THE AIRCRAFT. GROUNDED - YES. DIVERSION - FOUND LAV A RINSE VALVE CONTINUOUS FLOW. REPLACED RINSE VALVE REF B737-900 AMM 38-32-01 OPS CHECK GOOD NO FURTHER LEAKAGE NOTED.