Leaking coolant

It sounds like you found the drain tube for the pan under the heater core / AC evaporator. It's purpose is to catch the massive condensation from the AC removing the humidity from the air, but it will also catch coolant leaking from the heater core. If you see green coming out of that tube, suspect the heater core.

Caradiodoc

This is REAL common, ... On GM vehicles that use the red "Dex-Mud, ... Ah, ... I mean Dex-Cool antifreeze. Not so common on Chryslers and Fords. You'll read a lot about coolant leaks on this site, but remember, EVERY car on this site has a problem. The Taurus doesn't have any more problems than most other cars, at least in this respect.

It's kind of rare to lose the coolant so fast. One thing that can catch people by surprise is to have a plugged heater core causing no heat inside the car. They can usually be back flushed quite easily with a garden hose, but every once in a while there will be a hole corroded through the core that was blocked by the debris. That means the leak doesn't show up until after the mechanic flushes out the blockage.

The best thing you can do is replace the coolant every two years. Acids build up in the cooling system as a byproduct of combustion gases. That is hard to avoid so there are anti-corrosive additives in antifreeze to neutralize that. Antifreeze is alcohol and it will always be alcohol. It's those additives that wear out. When you have any two different types of metals and an acid, you have a battery, which means corrosion. You will find brass, cast iron, aluminum, lead and tin, (solder), and other metals in the cooling system. You can get an idea of how well or how little those anti-corrosive additives are working by measuring the voltage in the system. Use an inexpensive digital voltmeter with one probe on the engine block and the other one in the coolant by the radiator cap but not touching the metal core. Any reading over 2 volts is reason to flush and refill the system.

Caradiodoc