Click on Image for video Instructions: Obviously must be done in a closed space and above 50 degrees, also use warm water to activate! Can be purchased from Amazon.
This system releases a harmless gas that reacts with ordor -causing molecules and breaks them down, in a similar manner as chlorine splits apart ozone. Both chlorine and oxygen are very good at reacting with other molecules. The reviews indicate this is very good at getting rid of tobacco odors permanently. Cleaning and painting may still be recommended but this seems like a great place to start, especially if you are showing a house for sale.