[MetalMan]

Looks like I forgot to answer part of the original question.

If you only submerge Lipos in salt water, they won't be discharged much at all, but the positive (aluminum) tabs on the cells will dissolve in the salt water (salt water is quite corrosive). So that means that the cells (and the whole pack) would have a lot of energy left. Throwing away a Lipo pack with a lot of energy left could cause a pretty good sized explosion, would would be very bad for the guy who collects the trash.

Here's what I do, and I know that this method does a pretty good job of making the pack more safe to throw away.
-Discharge the pack as low as you can using any means you can. IE: the discharge function on a charger (set to NiMh with a low cutoff voltage), an electric motor hooked up directly to the pack, etc.
-Hook up a resistor like a 10ohm 10watt one to the pack (polarity doesn't matter for resistors), and let the resistor discharge the pack. Get the voltage as low as possible with the resistor (check with a voltmeter).
-Make a container with salt water in it, and puncture the battery multiple times. It should be safe to puncture the battery since all of the energy has been discharged from it. Then, stick the battery into the salt water solution, and watch the cells bubble.
The pack will be done in the salt water when bubbles no longer are being released. At that point the pack is "safe" to throw away.