[fingpilot]

The concern would be where was the water going to end up.

In my early DC-9 days, a light hair colored FA put a stopper in the front galley sink to wash something, started the water running, and got 'distracted'. She next reported (to me) that the water system was empty. She didn't mention that the galley sink had overflowed, and water had 'disappeared'.

The entire 40 gallons had run down the starboard side of the floor, thru the cabin floor channel, and emptied thru a drain into the main wheel well compartment. The cabin pressurization flows thru holes in the floor into the cargo bins, and then out the outflow valves back in the rear bin.

At 33000', was minus 55C that night. Water immediately froze as it swirled around in the wheel well, even with the gear doors closed.

My saying in those days was that the DC-9 actually did not stand for 'Douglas Commercial', but 'Direct Cable'. Every single control surface was hooked to the cockpit by a cable, some hydraulically boosted, some not. Flaps? Cable to the actuator valve. Trim? Direct cable. Engines? Direct cable.

Every one of those cables went thru the wheel well. They were all encased in rapidly solidifying ice. As the light bulb went off over my head, the autopilot disconnected itself, the trim had 'frozen'.

Long story short, a slow descent to below freezing level, all wing anti-ice on, and lots of prayers. We planned a no-flap landing, possibly emergency extend on the gear, and no thrust reverse.

By the time we got on final, we had everything back.

Once in the gate, I dropped the gear doors and turned on the well lights. It looked like a Swiss chalet in the dead of winter. There was 6" of free clearance around the wing anti ice ducts, and the bulkhead where the control cables ran was warmed up enough to allow them to move thru the solid block of ice. A perfect reverse shape of the gear, tires and wheels was the only space not wet and glistening.

Douglas issued an AD. They forbade plugging the sink, and removed the stoppers in the entire fleet.

To this day, I see F/A's using a cocktail napkin to plug the drain to fill the sink.