It seems to be common practice that when you autoclave liquids (or any flasks), you keep the lid loose to prevent pressure to build up. But after autoclaving as the flask starts to cool down isn't that create underpressure in bottle and start to draw in air from the room, which is not sterile. So I'm assuming that contaminate your flasks and liquids again? How autoclaved items (especially the liquids)should be packed and cooled down to prevent that happening?