If your talking about those attachments that go on the end of the siphon tube. You want to point side up so when wort hits that it makes it splash causing air by spreading it out more consistantly when transferring.
Pressure???? No comprende. YOu taliking one of those bubblers?,?Never really thought of that though but,now Im seing what you are making sense of ,like air in a balloon? Im interested in some other answers myself,now. HOw does that work for 30 min with an airtight seal? Wouldnt it be like pumping a bike tire up? It must not create enough pressure in the time frame.