Narrative:

Aircraft inbound flight arrived at ZZZ. I was asked by lead mechanic to assist mechanic in resolving an inbound pilot report that stated 'lav flooding M2 and first class.' I determined that the cause of the flooding was a blocked forward water drain line. This line drains the forward and mid galleys as well as lavatories (lav) A1; M1 and M2. After determining that the drain was blocked; I obtained MEL 38-02 for the forward and mid galley drains; and MEL 38-04 for the A1; M1 and M2 lavatory faucets. Maintenance procedures manual (mpm) 38-04 was accomplished; requiring shutting off the water to the lav faucets. This action prevented any additional water from entering the drain. The water in the fwd lav and M2 lav was cleaned. No water was visible in the lav sinks. No leaks were evident. The aircraft subsequently air interrupted for water coming from the M2 lav. After landing; I inspected the M2 lav and found the sink filled with brown water. Spilled water on the cabin and lav floor had been soaked up by blankets placed on the floor by the flight attendants. In retrospect it is apparent that on takeoff when the aircraft nose pitched up; water trapped in the drain lines flowed to its lowest point (the M2 lav) and spilled on the floor. Need a procedure to drain residual or trapped water from a blocked drain line prior to flight. No procedure or method to verify line is clear and prevent a future occurrence of the problem.

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Original NASA ASRS Text

Title: A Lead Mechanic reports about a B767 that arrived with forward and mid lavatories flooded from a blocked forward water drain line. Item was deferred; but lav flooded again during climb; the aircraft was subsequently returned to the departure field.

Narrative: Aircraft inbound flight arrived at ZZZ. I was asked by Lead Mechanic to assist Mechanic in resolving an inbound pilot report that stated 'LAV flooding M2 and First class.' I determined that the cause of the flooding was a blocked forward water drain line. This line drains the Forward and Mid galleys as well as Lavatories (Lav) A1; M1 and M2. After determining that the drain was blocked; I obtained MEL 38-02 for the Forward and Mid galley drains; and MEL 38-04 for the A1; M1 and M2 lavatory faucets. Maintenance Procedures Manual (MPM) 38-04 was accomplished; requiring shutting off the water to the lav faucets. This action prevented any additional water from entering the drain. The water in the FWD lav and M2 lav was cleaned. No water was visible in the lav sinks. No leaks were evident. The aircraft subsequently air interrupted for water coming from the M2 lav. After landing; I inspected the M2 lav and found the sink filled with brown water. Spilled water on the cabin and lav floor had been soaked up by blankets placed on the floor by the Flight Attendants. In retrospect it is apparent that on takeoff when the aircraft nose pitched up; water trapped in the drain lines flowed to its lowest point (the M2 lav) and spilled on the floor. Need a procedure to drain residual or trapped water from a blocked drain line prior to flight. No procedure or method to verify line is clear and prevent a future occurrence of the problem.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.