What's wrong with pouring it down the drain. I didn't see any toxic warnings when I used it last. It's used for dying cloths, and gets rinsed down the dran in that process. I'm not a fan of using the drain to dispose of questionable liquids, but this is one I wouldn't worry about.

Just be careful of your sink when you pour it down the drain. I your sink is aged a bit, you may dye the sink also. Make sure to use a lot of water when pouring it to prevent this from happening.

Let me know if I'm wrong.

Don