Vinegar is effective in keeping rats away. Vinegar is used in preventing rats from entering a home through pipes, including through the kitchen sink or toilet.
Use vinegar on a monthly basis for maximum effectiveness at preventing rat infestation through the kitchen sink. Pour one cup of baking soda into the drain in the kitchen sink. Follow this up with one cup of vinegar. Allow the mixture to settle for a few minutes. Follow up the baking soda and vinegar by rinsing the drain with boiling water. Both white and apple cider vinegar are effective. Use garbage disposals as little as possible and never dispose of grease down the drain.