Mechanically remove as much crud from the inside of the gourd as you can with improvised scrapers and brushes, then fill to within (appx) a quarter inch of the cork with activated charcoal
granules. NOT powder. Tilt and tap as necessary to assure full contact with the gourd walls.
Set the gourd in a secure stand and slowly add denatured alcohol (not the rubbing variety which contains a lot of water and perfumes) to the top of the charcoal with an eyedropper or the functional equivalent.
Do not get let the alcohol get within "wicking range" of the cork.
Wait a good while---several days---until the alcohol has entirely evaporated, and it will just pour back out. Maybe a few clinging bits but that's it. Brush them out and you're done.
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