Precautions for Testing Garbage Disposals:
To test a garbage disposal for leaks, turn it on and run water through it. The water load should be great enough so that any leaks will become apparent. A good way to do this is to close the drain and fill the sink with water before releasing the stopper.
While testing a garbage disposal, never put anything other than water through it. Before turning it on, check to make sure there are no objects already in the disposal.
If a dishwasher is connected to the disposal, make sure that the line that connects them is securely attached.
Check to make sure that the garbage disposal is connected to a drain that is 1½ inches or greater in diameter.
Check to make sure that the disposal is provided with an adequate water supply.
If the home has a double sink, check to make sure the waste pipe from the disposal has a trap installed.