C.  Engage drain nipple with waste duct and position drain nipple against heater gasket as follows:
(1)  
At forward service panel, position drain nipple with flapper valve open/close levers up and slightly forward.

(2)  
At aft service panel, position drain nipple with flapper valve open/close levers up.

D.  Install mounting bolts.
(1)  
Install nut ring from behind service panel.

(2)  
Dip bolts in sealant.

(3)  
Install bolts while sealant is still wet.

E.  Install clamp to secure waste drain duct to drain nipple.
NOTE:  To ease clamp installation a minimum of one wrap of teflon tape can be installed to waste drain duct clamping point. Check existing tape and replace if necessary.
F.  For forward service panel, install aft access door on right inner wall of nose wheel well.
G.  For aft service panel, install aft cargo compartment aft bulkhead lining panel.
H.  Close flapper valve in waste tank drain nipple.
(1)  
Rotate CLOSE lever in direction of CLOSED arrow (toward drain nipple centerline) and hold lever in closed position.

(2)  
Move OPEN lever slightly in opposite direction of OPEN arrow (away from drain nipple centerline) to lock flapper valve in closed position, then release both levers.

6.  Restore Airplane to Normal
A.  Add flushing chemical to waste tank (Ref 12-17-00).
B.  Close waste system service access door.
C.  Close the following circuit breaker and remove DO-NOT-CLOSE identifier:
(1)  DRAIN HEATER
D.  Remove electrical power if no longer required.
500 
Feb 20/89  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  38-32-81 Page 403 

WATER TANK PRESSURIZATION SYSTEM - DESCRIPTION AND OPERATION
1. General
A.  The water tank pressurization system provides air to maintain pressure in the water system. The pressurized air is normally provided simultaneously by two sources. If both sources are not available, either is capable of providing tank pressure. The two sources are listed below:
(1)  
A bleed air line direct from engine No. 1 (Ref Chapter 78, Exhaust).

(2)  
The pneumatic manifold, which is in turn pressurized by: either or both engines, the APU, or a ground pneumatic cart (Fig. 1).

B.  An alternate way of pressurizing the water tank on the ground is by connecting a pressure source to the air valve on the water service panel.
C.  All water tank pressurization system air passes through an air filter and pressure regulator on way to the water tank. The air is filtered to prevent contamination. The pressure regulator reduces the air pressure and maintains 25 psi in the water tank. Check valves in the system prevent reverse pressurization (Fig. 1 and 2).
2.  Pressure Regulator
A. The pressure regulator is installed above the water tank aft of the aft cargo compartment (Fig. 1). The pressure regulator reduces the air pressure from the No. 1 engine to 25 +2 psi.
3.  Air Filter
A.  The air filter is installed above the water tank aft of the aft cargo compartment (Fig. 1). The filter contains a replaceable 10-micron filtration cellulose element. It filters all air entering the air pressure regulator.
4.  Pressure Relief Valve
A.  The pressure relief valve is installed above the water tank aft of the aft cargo compartment (Fig. 1). The relief valve prevents the water tank from being damaged by overpressurization. It is set to relieve at 50 +2.5 psi. Reset pressure is 37 psi minimum.
500 
Feb 15/79  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  38-41-0 Page 1 

F92983 T54480
 Water Tank Pressurization System  577 
38-41-0  Figure 1  Aug 15/80 
Page 2 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

506  Water Tank Pressurization System Schematic 
Feb 15/79  Figure 2  38-41-0 
Page 3 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

WATER TANK PRESSURIZATION SYSTEM - MAINTENANCE PRACTICES
1.  Water Tank Depressurization-Pressurization
A.  General
(1)  
The water tank is normally pressurized by engine bleed air coming through a direct line from engine No. 1 and by air from the pneumatic manifold. Either of these two sources can maintain tank pressure. The pneumatic manifold can be pressurized by either or both engines, the APU, or a pneumatic ground cart.
　
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