Waste disposal can be drained from the aircraft in flight and on the ground. Waste water can be removed through the lavatory waste service door. The system can drain the waste water from the sinks and lavatory overboard through the heated drain lines and the drain masts.

The waste disposal system lets waste water flow overboard through drain lines and drain masts or to the waste drain valve in the lavatory waste service panel.

The drain masts ensure the waste water drains clear of the aircraft. The configuration of the water/waste components and controls, other than the drain masts and lines, can differ for each aircraft. A completion center installs this equipment, and as such, is not included in this manual.

The forward drain mast includes a drain mast and an internal heater. The heater prevents waste water from freezing in cold conditions. It is installed about the center line at FS396.00 and is attached to the fuselage skin with screws. There is one drain line to the forward drain mast.

The aft drain mast also has an internal heater. It is installed about the center line at FS655.00 and is attached to the aft wing-to-fuselage fairing with screws. There is a lavatory vent line and a sink drain line attached to the aft drain mast.

The lavatory waste pipe moves waste fluid from the lavatory system to the valve in the lavatory waste service panel. The pipe is of composite material and has an operating temperature range of –53 °C (–65 °F) to 71 °C (160 °F). The operating pressure of the pipe is 8.5 psi (58.6 kPa).

The lavatory rinse/fill hose moves fluid from the valve in the lavatory waste service panel to the lavatory system during replenishment.

It is an insulated rubber hose clad in a metal braid, terminating with two metal couplings. The hose has an operating temperature range of –53 °C (–65 °F) to 71 °C (160 °F) and an operating pressure of 125 psi (861.85 kPa).

The heated drain hose moves fluids from completion center-installed equipment to the forward drain mast. It is an insulated rubber hose clad in a metal braid, and terminating with two metal couplings.

The hose has an operating temperature range of –53 °C (–65 °F) to 71 °C (160 °F) and an operating pressure of 125 psi (861.85 kPa). There are heater coils around the hose between the aft wing-to fuselage fairing and the aircraft skin. A thermostat attached to the hose is set to start heating the hose at 4.5 °C (40 °F) and stop heating at 18.3 °C (65 °F). The heated drain hose usually gets its power from the right main bus.

The lavatory vent hose ventilates the lavatory system. It is an insulated rubber hose clad in a metal braid, terminating with two metal couplings. The hose has an operating temperature range of -53 °C (-65 °F) to 71 °C (160 °F) and an operating pressure of 125 psi (861.85 kPa).

The lavatory waste service panel is used to service the lavatory system. It has the valves for the lavatory drain pipe and a rinse/fill hose and handle for the lavatory control release cable. The valves and cable supply the interface for the ground crew to service the lavatory system.

The heated drain hose and lavatory drain hose move waste water from the respective completion center items to the forward and aft drain masts. The drain masts get electrical power from the right main bus. Signals from a completion center-installed controller opens and closes the forward and aft drain mast heater relays in junction box No. 2. This energizes and de-energizes the heating elements in the drain masts and lines.

Warning:
Make sure that the drain mast is cool before you touch it. The drain mast can be very hot and can cause burns to your hands.