boil 99% isopropanol ( with plenty ventilation, either outdoors or with giant fans blowing the vapor outdoors) by immersing pyrex glass container (dont use mason jar they crack with heat) in simmering water, hot enough that its near boiling, so that the isopropanol begins to boil.. then add your DMT fumarate, stir while it boils, and add more 99% isopropanol until all the dmt fumarate dissolves
stir for at least 5 min intervals after adding more isopropanol to see how much more dissolves before adding more, since it takes a lot of time to dissolve even when you have enough solvent.
when all dissolved ,should look completely clear, colored yellow with impurity
put somethign overtop to slow evaporation and allow it to cool down to room temperature while disturbing as little as possible. What can happen can vary here sometimes depending on how concentrated it is.. the first crop of dmt fumarate can crystallized out and bring a lot of the yellow color back out, you are left with a colorless solution, put that solution in the freezer for 3-4 days, and it will give you a second smaller crop of highly pure colorless dmt fumarate, you can repeat the process with the yellow fumarate if you like even decolorize with activated carbon if you are ok with losing some yield