I use one for melting wax. Make sure it is the kind with the removable crock. I do add water the first melt. Then I pour the whole thing into one of those aluminum big square pans they use for banquets (I get them at Costco). Let it cool then just lift out the wax, set it in a collander to dry.
Then remelt, strain through sweatshirt material (fuzzy side up).
I melted some old dark comb this past weekend. More junk than wax. I will now just toss the old comb, wasn't worth the hassle.
I also get those great big aluminum "oven liners" they sell for electric ovens. I put it on a rack just like a cookie sheet with an empty old frame on it, set the oven for 225-250. Melts the wax and stuff right off. It just takes a few minutes, so don't leave and watch it.
I did try melting wax on the stove using double boiler method. Too scary for me. I have a gas stove.
Never leave your wax alone, even in the crock pot.