I. Put the Airplane to Its Usual Condition
 S 432-018
 (1)  
Install the galley drain line strainer, if it is applicable (AMM 25-31-13/401).

 (2)  
Flush the drain system with clean water.

 (3)
Do a check of all the drain line connections for leaks.

 S 152-019
 S 722-020
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A
747-400 MAINTENANCE MANUAL
 DRAIN MAST - REMOVAL/INSTALLATION
_________________________________
 1.  General_______
 A.  This procedure includes two tasks:
 (1)  
The removal of the drain mast.

 (2)  
The installation of the drain mast.

 B.  The drain mast is on the bottom of the airplane, left of the centerline, at station 865. Open the access door adjacent to the drain mast to get access to the top of the drain mast.
 C.  References
 (1)  
AMM 25-52-04/401, Containerized Cargo Compartment Insulation

 (2)  
AMM 30-71-01/401, Ribbon Heaters

 (3)  
WDM 30-71-11, 30-71-12

 D.  Access
 (1)  
Location Zone 123 Forward Cargo Container Compartment Aft Half, Left 191 Fairing Wing to Body, Forward Lower Half L

 (2)  
Access Panels
 191T Access Panel, Drain Mast

 TASK 38-31-61-004-002
 2.  Drain Mast Removal__________________
 A.  Procedure
 S 864-001
 (1)  
Open the fill/drain valve to release the pressure in the water tanks (AMM 12-14-61/301).

 S 864-003

 (2)  
Open these circuit breakers and attach DO-NOT-CLOSE tags:

 (a)  P414 Power Distribution Panel - Left 1) 414A24, WASTE & WTR LINE HTRS - MAIN POWER 2) 414C21, DRAIN MAST HEATERS - GROUND SERVICE MODE 3) 414D5, WASTE & WTR LINE HTRS - MAIN POWER 4) 414L23, DRAIN MAST HEATER - AIR - CENTER
 S 014-004
 (3)  Open the door adjacent to the drain mast to get access to the drain mast.
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A

747-400 MAINTENANCE MANUAL
DRAIN MAST ACCESS DOOR
DRAIN
MAST

SEE A
BONDING TUBING
JUMPER CLAMP
RIBBON
HEATER

DRAIN MAST DRAIN MAST HEATER WIRES TUBING
TUBING
CLAMP

BEARING PLATE (PART OF THE FAIRING)
ACCESS MOUNTING DOOR NUT AND WASHER DRAIN MAST FAIRING
FWD
A
Drain Mast Installation Figure 401
C79788
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A
747-400
MAINTENANCE MANUAL

 S 014-005
 (4)  
If it is necessary, remove the insulation blankets from the drain mast area to get access to the drain mast (AMM 25-52-04/401).

 S 034-006

 (5)  
Disconnect the bonding jumper for the drain mast.

 S 014-039

 (6)  
If it is necessary, remove the ribbon heater to get access to the tubing clamp that is just above the drain mast (AMM 30-71-01/401).

 S 034-007

 (7)  
Loosen the lower tubing clamp and move the clamp away from the drain mast.

 S 034-008

 (8)  
Disconnect the drain mast tubing from the drain mast.

 S 034-009

 (9)  
Disconnect the heater wires for the drain mast.

 S 034-010

 (10)
 Remove the mounting nuts and washers.
　
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