Do you mean that the flask will break just from the pressure of the inserted hose, or due to expansion during a reaction?
What if I not jam the hose in but leave it lightly inserted and seal around the flared lip of the flask?
I really just don't want any leaks. I'll probably seal with silicone, followed by an electrical and duct tape wrap.
And, no, I'm not making a PP device, just using a braided PVC hose with a thick balloon at the end (which happens to be colored all psychedelic-like... it's called a "marbleized" ballon. Too bad the reaction won't/shouldn't produce a psychedelic compound).