What I do is to place crude DMT in a small beaker (i.e. shotglass), then pour over it minimum amount of solvent (naphtha, heptane etc.) - just enough to cover the spice and little extra. I place the beaker in a hot water bath and stir the spice. I can add little bit of solvent until all the DMT is visibly gone. What is left on the bottom is usually brown sludge. I carefully decant the supernatant solvent into a Pyrex dish and repeat the procedure with fresh solvent.
I repeat this several times until no DMT precipitates on pouring. You can test this by pouring a drop on a glass and when the solvent evaporates, it should leave little to no residue.
Then I close the Pyrex dish and freeze-crystallize the now purified crystals.
Don't worry about using little more solvent, most will still crystallize out of solution assuming you used naphtha or heptane.
Even evaporating the solvent will yield much purer product since most of the impurities have way lower solubility in the solvent than DMT.
Note the brown residue is still active and can be used as long as the impurities are not harmful.