I've not done it in a crock. (BTW a crock lets the air out - like a burp, but doesn't let air in which can halt the fermentation process and expose the kraut to outside pathogens.) I use glass jars I picked up from Cost Plus that have hinged lids with rubber gaskets. These work quite well. There is just enough "give" to allow the jar to burp if need be. They are relatively inexpensive as well. The crocks I've seen somewhat prohibitive in price for my limited budget. The jars are multi-use as well (important in my small kitchen). I do have a friend who has a crock and has made quite lovely sauerkraut with it.