my single kitchen sink is backing up with water but will drain when I use the disposal. It takes a few seconds for it to start backing up again after I turn the disposal off. I took off the p trap today and it was clear. I used vinegar and baking soda without much success. I have plunged extensively without improvement. I have reached into the disposal and the blades are turning fine, I also have used an allen wrench on the bottom of the unit without any difference. I have also reset the disposal. My feeling is that the disposal is not the problem but maybe something further in the pipe. It does seem to connect to the dishwasher(which drains well) about 5 feet away. Help?