Re: Bad draining kitchen sink
More than likely there is a partial blockage in the horizontal ( lateral ) run in the wall.
With a disposal and/or dishwasher they inject all sorts of grease and garbage into the drain lines. When all that debris builds up the inside of the pipe starts closing and clogging the lines. There will be enough of an opening to allow the water to flow from the sink but when the dishwasher and/or disposal run they are pumps --- more volume and more pressure plus the partial blockage = back up
Removing the "P" trap and snake the line should clear things.
Hopefully this helps.
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