In a pinch, "clean" sippy cups with mouthwash

Thorny's got a great travel hack, and she tells a good story, too:

We stayed in a hotel while visiting family, and were back in our hotel room. Our twin boys were clamoring for their pre-bedtime cups of milk, and while we'd managed to find a convenience store open to buy some milk, there was no dish soap to be found, and we'd forgotten to wash the kids' cups before we left my aunt's house. Normall...