Sterilize a 5L Flask

Glass stovetop too?!

 

No, the stovetop was fine, but the flask died violently.

 

I would not boil on an electric coil. I lost more than one flask before I learned my lesson.

The lesson that convinced me never ever ever ever to do that again was awful. I had boiled the starter on the coil, all was fine. It was before I had a stirplate so before bed I swirled the starter. The bottom gave way and the nearly finished yeast starter was evenly distributed all over the kitchen floor. What a horrific mess! Never did that again.

But to give an answer to the op the pressure cooker is probably the best, like an autoclave. I do like billandsuds vodka approach, never thought of that.