When dealing with rudimentary preservation solutions, such as a Vacu Vin or even a basic stopper, the seal that is made is not 100% airtight. However because the air has either been sucked out of the bottle of has been displaced by an inert gas, the seal is completely sufficient to protect the wine. Some folks will put a stopper on the bottle and then try and lay it back down in their wine cellar. If you have done this in the past you are already aware that after awhile some wine will in fact leak out. So you really want to have your bottles standing upright after they have been preserved to avoid that. And yes, if you turn the bottle upside down not only will the wine probably leak a bit, but the stopper may loosen up and even fall out... and that is just a waste of good juice!