If it's MHRB, then the yellow stuff is some plant fats, other random minor chemicals from the root, and some other alkaloids.

You can separate out purer dmt from that other stuff by recrystallizing. For example, if you heat up a crude extract in 25-100ml of naptha per gram, and you heat it up past 40C or so, the dmt melts into a yellowish blob. If you stir it all up it will all get mixed into the naptha, but if you just let the blob sit on the bottom, most of the dmt will get dissolved in the naptha. By heating it about to the point where it's uncomfortable to touch the glass with bare hands, the majority of the dmt gets dissolved into the solvent. Then you can pour off relatively clean solvent, leaving a little yellow glob behind. Either evaporate the solvent or freeze it to recover your cleaned up DMT. But the leftovers are also kind of interesting.

That stuff is sometimes called 'jungle spice'. It will still contain some dmt, but also a larger proportion of the other stuff. Smoking it apparently results in a different experience than pure dmt. You can read a bit about it here: https://wiki.dmt-nexus.me/Jungle_Spice