My disposal only hums when turned on and doesn't drain properly. I have looked inside with a flashlight and see nothing that appears to be jammed in the blades. The hex wrench that came with the disposal and was taped to the side of it is missing. Can an ordinary hex wrench be used to turn the blades from below? If so, what size is needed? If it is a proprietary wrench that only comes from whirlpool, please tell me how I can obtain one.