I found this 2 yr old thread here, and instead of bumping it will just reference it here. 
https://www.dmt-nexus.me...mp;m=1052317#post10523171) I just want to make sure this 
flask is fine. I would not use the included rubber stopper though. 
Hailstorm in the above thread says that using a magnetic stirrer (which I have) and NO STOPPER is the best way to go.  So from that, I can surmise that you would not want a cap on at anytime during the extraction process as you would be stirring and not shaking the contents of the jar. 
2) OR, I could opt for this 
brewery stopper that has a large hole in it, allowing the solution to vent minimally. 
These are the final questions I have before introducing the rough draft of my TEK and starting my first extraction, which I am not rushing in anyway. Thank you. 
 🌳👨🔬🌳 - My A/B Hot Plate TEK  - 🌳👨🔬🌳
 🍜🍜🍜 - Don't Heat Your Naphtha, Heat Your Soup! - 🍜🍜🍜
✴✴✴ - 
White Spice vs Yellow Spice - 🌟🌟🌟
"You are an explorer, and you represent our species, and the greatest good you can do is to bring back a new idea, because our world is endangered by the absence of good ideas. Our world is in crisis because of the absence of consciousness." - Terence McKenna 🙌 
"Dang, that's really impressive for a first extraction.  Those xtals are nicely resolved." - Benzyme  🙌