If you get a sewer smell when you are using the dishwasher on a kitchen sink, it often means there is a blockage in the vent or the drain of the pipes inside the wall. If you have a clogged vent on the roof, then the back-pressure that is created when you try to put water into the pipe, will slow the water down and it will begin to clog the pipe. In order for water to enter a pipe, it has to have an open vent on the roof of the house. This is a pipe that is attached to the drains, but instead of running down to the city, runs up to the roof. Since both water and air take up volume in the pipe, in order to put the water into the pipe, you have to push the air aside. 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.