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I tried those but it was very slow to filter. I just used a regular mesh filter. It doesn't bother me to have tiny bits of chocolate in my liqueur.
Mine lasted the whole time I had it in the fridge. About 3-4 mo.
I had no problem finding the 190 proof Everclear. If you use a sweet baking chocolate add less sugar. If it's unsweetened you may need slightly more. Just make sure it's a good quality baking chocolate. I found this to be similar to the Godiva chocolate liqueur. It's really very good.