In large Dutch oven, place pork, bay leaves, salt and 1 cup water. Cook over medium high heat and bring to a boil. Turn temperature down to low, cover partially and simmer for 1 hour, or until pork is tender. After one hour, uncover, continue to simmer and let all the liquid evaporate.
As the liquid evaporates, the pork will start rendering its fat. The fat will accumulate on the bottom, remove all but 2 tablespoons fat.
Continue to cook pork until it becomes crispy, and the meat becomes so tender than you can smash with the spoon and the meat starts to shred. Cook until you can shred all the meat, another 15-30 minutes.
While pork is cooking, seed and devein the chiles. Place in a deep bowl and top with boiling water. Cover and let them soak for 10-15 minutes, or until chiles are very soft and pliable. Fish them out of the water and reserve a bit of the soaking liquid (about 1/2 cup).
Place chiles and soaking liquid in blender container, along with garlic, cumin, and oregano. Blend until very smooth.
Add chile sauce to the pork and mix well. Add salt, pepper, and vinegars. Mix well and simmer, stirring every few minutes, until sauce becomes a deep red color, about 15-20 minutes. If sauce starts to stick at the bottom of the pan, add a bit of water.
Adjust seasoning and serve hot with flour tortillas and salsa.