I just purchased a little cap that is used for pickling, or making sauerkraut, and I just love it ! There are several different companies that make these caps, so they go by several different names. I am just now learning how to make fermented veggies, and started my first batch of sauerkraut, and it is in a regular wide-mouth mason jar and using the pickle pipe. They are a soft plastic lid that has a little escape valve on it that sticks up, and it lets the gas escape out of the jar; but keeps everything from getting into the jar. This way, there is no chance of the jar building up enough gas pressure that it explodes, and still it is securely closed. I got mine from one of the Amazon review sites, but there are several types of these available on the internet. Here is a picture of my cabbage in the jar with the pickle pipe, and ready to start fermenting into sauerkraut.