Question: My kitchen sink (where the garbage disposer is located) smells bad whenever the dishwasher runs. Why is my kitchen sink emitting a sewer smell, and how can I stop it?
Answer: If your kitchen sink drain is emitting a sewer smell whenever you run the dishwasher, you have a blockage either in the vent or the drain related to the sink and the dishwasher.
This is probably caused by a clogged vent on the roof. When the roof vent is clogged, back-pressure is created when you run the dishwasher which slows the water down and it will start to clog the pipe. Since both water and air take up volume in the pipe, something needs to push the air aside so the water can run through. The vent redirects the pressure up to the roof at the same speed the water is flowing. So if either the drain or the vent are clogged, then there is no place for the water to go without first forcing the air back into the room, which is combined with sewer gas.
What You Can Do
Hire a plumber to fix the venting from your kitchen sink or who can clear the vent clog.