When you search the 'net, you find the salt water method but if you dig a little, you'll also find that it's no longer preferred way to get a lipo ready for disposal. Testing has revealed a prob with corrosion of the cell tabs or connections - salt water corrodes them quickly enough that the lipo is not fully discharged before the cell tab is corroded off. So if you're going to go with salt water, you need to puncture cell membranes to let the salt water contact the media.

What is now recommended is to take a single 1157 automobile tail light bulb and discharge the lipo for 24hrs. Do it outside as this will likely cause puffing if its not already puffed, After 24hrs, lipo is dead, harvest connectors, then connect the pos and neg and throw it away, or take it to a battery recycling center. Lipo in this condition is supposed to be landfill safe.

http://www.rcgroups.com/forums/showthread.php?t=752866