I'm with Flotsam on this one. Been using soda bottles and a technique similar to his for years and they have always worked well for me. Instead of leaving the bottle half full though, I top off the partially full bottle with propane gas from a soldering torch. Being heavier than air, it acts like a gaseous floating lid over the contents of the bottle and keeps the O2 out. There is a product available specifically for this purpose and I'm told that it is nothing more than butane. Problem is that a small can of the stuff goes for over $10, while you can get a small propane tank for about $3 to $4 US that will last for months.
The accordion bottles are a waste of time and money. They don't seal well and are hard to handle when full.