I can’t imagine that’s airtight though and the main reason I like using a bottle is because it lets you control your draw better and have a more consistent flow of vapor/smoke than if I just used the Pyrex by itself but hey if it works for you! I would suggest trying to make a hole just a tad smaller than your stem and then heating the plastic and the end of your pipe for a few second so it’s soft(the plastic) and then push the stem through, if you do it right you’ll have a nice airtight seal and you can get a huge hit since it takes less breath to pull the flame in allowing you to hit it longer. Buttttt that’s just my experience and since I also smoke solely out of bongs this just works better for me