What do you put in a airlock?

[trucknut]

I read an article on how oxygen can exchange thru the water in the air lock. In my long term ( just started last month ) carboy air lock, I use vodka - glycerine- k-meta mix. On top of the air lock I use a sterile loose fitting saran wrap with rubber bands to seal. This way the air exchange is limited, but allows a bit of in out expansion contraction and should stop (slow) the evaporation. This would keep out the fruit flies, dust and other contamination. That is how my long term carboys' will be sealed. A little piece of mind while on holidays.