So, I ran an experiment.
Cleaning chocolate with
- Club Soda
(carbonated water with potassium bicarbonate & potassium citrate) - De-bubbled Club Soda
(hand blender... excellent de-bubbler, a hit with the kids) - Tap water
And, the rest came off by just tossing it in the washing machine. So, perhaps my experiment was flawed ... I needed a tougher stain? Or this rag was too easy a fabric? Or I didn't work it in enough and let it set? A chair's cover definitely remained stained the last time we had a chocolate-a-splosion.