It stains skin (and other things) and burns soft tissue, so be careful.
Eye protection is highly recommended.
I don't know that I would pour it down the drain, not because of any hazard, but because it could stain your sink. In the quantity you're talking about, if you dilute it with water, disposal isn't a problem. I would probably dilute it and place it in the sun for a day and then after it decomposed, pour it outside on the ground away from any water sources.