I've been figuring this one out a bit at a time. I get a piece of advice here or there and then of course there's my tried and true:
Trial and Error
I had some nice and dry cappings from a few seasons ago. That season I'd had the bees lick them dry.
When these were melted in the crock pot everything went great - the wax was clean with very little debris.
Then I remembered that the dross and honey go to the bottom of the pot and the wax floats to the top. So I switched to a two stage process.
[Photo - glass pitcher with debris caught on silk.
The clean wax pours from the spout onto the second silk which is clamped on my mold container.]
Stage one to melt the wax. Then I poured it through a piece of silk into a glass pitcher. The crud was caught on the silk.