Food grade plastic buckets and lid also work well for sauerkraut. Coupled with a 3/8" rubber grommet,plastic air lock and cool basement you can produce some very good results.
Here's the one I got. Kind of an extravagance admittedly. There are many similar or, as Dave says, a 2" dowel would probably work just as well. Or an old baseball bat.A link to the stomper please the potato masher works there was a thread on here a member used a sledgehammer with a plastic bag on it. Don’t think the ceramic crock would like that though:(