If your mouth wash comes in a plastic bottle then one way to reduce your plastic outlay is to switch to green tea and drop the gargle.
Dr. Michael Greger at Nutritionfacts.org summarizes studies showing that green tea is as effective against plaque formation as over the counter mouth washes.
What’s the Best Mouthwash? http://nutritionfacts.org/video/whats-the-best-mouthwash
So to fight plaque and plastic – drink green tea.