Peroxyl is a mouth wash/mouth rinse made up of 1.5% hydrogen peroxide mixed with water and peppermint-ish flavor. You use it when your mouth hurts - canker sores, aching gums and the like.
"Peroxyl" is sold by the Colgate company, but you can make your own by taking a teaspoonfull of 3% dilution hydrogen peroxide (what you get at the grocery store) and adding a teaspoon of water. If you want it to taste a little bit better, substitute Scope for the water. Swish around your mouth for a minute and spit it out. Try not to swallow, hydrogen peroxide kills cells (which is kind of the point).
Ah, the many uses of hydrogen peroxide.