Back in the day I would soak my bottles in my bath tub
with bleach water and then clean them the next day. The labels would fall off.
Nowadays I will be using the sun oxy cleaner (oxyclean ripoff) instead of bleach. Since the bathtub is not used by anyone, it will be easy to keep sanitized.
Also, an obviously simple suggestion: rinse your commercial beer bottles after you drink them and the mold won't be an issue.