Airlock - Twin Bubble
Also called ripple airlock, the twin bubble airlock lets CO2 out while preventing oxygen, dust, bacteria, bugs, etc. from getting in your fermenter. Fill half-way with water or sanitizer and put it on the top of your fermenting bucket or carboy.
A must for any homewinemaker or homebrewer. We like the twin bubble style air lock the best for long-term fermentations, such as wine or high gravity beers. The Three Piece Airlock is great for homebrewing as well.