You got that right. Its heat of solution with water is highly exothermic and has been know to shatter "turlets" too, as Archie Bunker would say.From my own experience don't put Draino in any bottle, I did this years ago to an old square short ink bottle and it exploded from the heat. Luckily it was in the basement on a concrete floor. Once I poured the water in it heated up really fast and shattered.
I'm glad you weren't hurt in that incident.
EDIT: I went back and read Glasshopper's post. The key to using Draino, as he said, is to "pour the mix" into the bottle. I read this to mean, mix the two components in a plastic container, and let cool, then you'd be good to go. As long as you don't introduce the two to each other in a breakable vessel, everything should be fine.