The S-Shape Airlock is a good choice for containers between 1 and 5 gallons in volume or when a slow fermentation is expected on larger batches. With this particular air lock you can detect even extremely slow fermentations on larger batches. This air lock is great for both wine and beer brewing; just fill it approximately half way with water and let the water act as an environmental barrier to keep bugs and other unwanted materials out of your batch while still allowing gasses to escape the fermentation.