Agreed Kristine. My mother always had a jar by the stove for pouring in the bacon fat (my father always had bacon & eggs for breakfast), and I have followed that example. (Didn't every cook back in the 50s, and before, have a jar like that?)
One other thing about rendering fat in the slow cooker, it works perfectly well if you just bung it in, and let it do it's thing, but it goes a bit faster if you have the patience to cut the fat up a bit. I will put 2# or so through a meat grinder, but when I got a 5# bag of leaf lard from a local pig farmer I was too lazy to go that route. I had to do the cutting work at the other end, as I wanted smaller cracklings, but that was easy.