Loose Vacuum Line Solution

[mgambuzza]

I was so excited when I discovered plugging in the line pictured in the center nut that my wiper actually worked(thankfully after getting some estimates for a wiper motor rebuild). The problem is how do I get it to stay? I tried loosening the nut, pressing it in, then tightening it. I didn't want to over tighten it and shear anything, and after a couple rides it popped out again. Is there something I need to do to keep it from popping out?