Salt water is not good for draining a lipo. A lot of times the the salt water will corrode the tabs, breaking the connection. This makes the pack seem like it has 0 volts when in fact it does not. Best method to dispose of a lipo is to hook it up to a small light bulb and let it drain to zero volts. Then twist the positive and negative leads together and toss in the trash. Of course let it discharge in a fire proof area.

Or the more fun route is to drive a nail through the pack and watch the sparks fly!