In a large skillet, brown the bacon over medium-high heat. Remove from the skillet and chop. Set aside. Reserve the bacon grease.
Return to the skillet with the grease, and add the onion. Cook over medium heat until the onions soften and brown, slightly.
In a large bowl, combine the beans, mustard and BBQ sauce. Taste the mixture and adjust the ingredients to taste. Stir in the onions and bacon. Slowly stir in the soda. You don’t want to much, which will make the mixture too runny.
Add to a crock pot and cook on high for about 40 minutes, or until warmed through and bubbling, stirring occasionally. Serve warm.