I purchased this jar system below. It has a way of releasing the gases through the chamber shown at the top. I liked the idea that since this is 1 gallon size I would force myself to make a lot of it and would therefor need to eat it. 🙂
You should get some glass mason jars to store the kraut once it is completed so you can start a new batch. The longer you ferment the cabbage, the more effective the bacteria. So you definitely want to get it out of the large jar and into the mason jars, so the new batch can ferment longer.
If you don’t get a system like the pickelmeister, you should figure out a way to get a cover for your jar that can release the gases.
It’s not entirely bad to buy some sauerkraut from reputable health stores as long as it is Raw and not pasteurized. Whole foods has several different brands that are raw and sometimes they can be had for a decent price. The have several that have just cabbage, salt, water and some other sea vegetables.