Danielle got me an awesome fermenting crock to make sauerkraut this winter and pickles next summer. I tried kraut once before and it was banned from the house. I was making it in a bucket and scraping the scum off the top. The fermenting crock has a water seal that keeps bacteria and mold spores out so you don't have the scum problem. It was a bit bigger than I was expecting. See the jar for reference. It came with weights on the left that hold the cabbage down and surprisingly had 2 lids in the box. I'm not sure if it was supposed to have 2 lids or if it was mis-packed. Nowhere in the webpage does it say it comes with 2 lids. I guess they think you will break one. To top it all off, it's made in Ohio by the Ohio stoneware company.
You fill the ring with the water and put the lid into the water. The fermenting gasses can escape but nothing can get in. For the brewers out there, it's the same concept as a glass airlock.
With lid down.