Eliminating plastic bottles in the bathroom is an ongoing task in our house. The worst offenders are the items we use least frequently, mouthwash being one of them. The key with this swap was to go for something more compact.
These little green Georganics mouthwash tablets are dissolved in 20ml water; they fizz like a dispersible aspirin, and then turn the water bright green. A 20-second rinse is all you need. I chose spearmint ,which lacks that really ferocious menthol taste of a supermarket brand. It's a bit more clove-y, which is bearable despite the fact I'm not a big fan of cloves.
Not only is this product free of plastic, but it will be a dream to take on holiday -- that's assuming bright green tablets don't attract the wrong sort of attention at customs. In fact, by the end of Plastic Free July, I'm pretty sure I'll be able to go on holiday with all the essentials, without plastic, and without all the heavy liquids I usually cart around.