Dissolve yeast in warm water, and then mix all ingredients in a one gallon crock. (Do not use a metal container. ) Cover with a close-fitting lid and let the starter rise until light (12 hours in warm weather, longer in cool weather). Do not let the starter get cold, ever. After using part of the starter, add one cup warm water, two teaspoons sugar, and enough flour to mix to the starter's original consistency. Add more potato occasionally as food for the yeast, but don't add more yeast. Use daily for best results. Starter improves with age.