Sorry, no filter for recipes by Crockpot/slow cooker, just for books. Those recipes will generally fall under Stews & one-pot meals. You will need to set up a bookmark for slow cooker and add recipes as you come across them.
I would also like to see a filter for slow cooker meals. I'm not sure if this may be an option, but I think it would be a great addition.
The problem is with adding any new filters when we are this far into the process - 700,000 recipes - is that is not practical for us to go back and add tags to all the recipes we have already indexed. If we added the filter now and just added it to new books we index, then members would find it odd that slow cooker recipes in their books (that had been indexed earlier) were not appearing in their search results. This is why is it probably easier for you to add your own Bookmarks.