You might want to try evaporating your naptha down a bit until its clouding at room temperature. IE it gets milky, especially when you blow air on it, that way you know for sure its saturated and will properly precipitate it when you freeze it. Sometimes if you use too much naptha, theres enough solvent to keep a significant amount of dmt soluble even when frozen, so you get very little in terms of precipitation/crystals.
I really don't like filtering with a coffer filter, or anything for that matter when freeze precipitating. I just pour off the naptha/heptane into another glass jar, even if theres chunks, and let it evaporate down until its clouding again at room temp. Then freeze it again and repeat until theres no naptha/heptane left. Your xtyals will be less pure the more you evap the naptha (since its concentrating the impurities), but filtering naptha is a royal pita imho, and you lose some product no matter how careful you are.
And as for it turning to goo when you scrape up the crystals, let the jar with the crystals stuck to the sides dry overnight, then scrape. That always prevents gooey crystals ime, and allows any residual naptha to evaporate. Just keep it in a cool dark and dry place, possibly with a small fan blowing lightly across the top of the jar.
You won't have to filter at all doing it this way, you won't get gooey crystals, and if you evap/freeze/evap/freeze/ect you can get all the dmt to precipitate as crystals and not goo. You just need an extra jar since one will have crystals drying in it while the other is in the freezer. After the first jar drys, and you have scraped, pour the naptha from the second jar into that one and let the crystals in your second jar dry while the one you just poured the naptha into evaps/freezes.
