So all I needed was a little patience!
amor_fati was absolutely correct. I ended up with 10.38 grams of well washed DMT-fumarate.
I am still a little surprised at how different it looks now, compared to before the water wash. Since I had already washed most of the excess fumaric acid away with acetone, it seemed like what I had at the end of the water wash process would be just about exactly what I had at the beginning.
The color was definitely more red/brown. It was yellow/brown before.
I also expected to see crystals forming in the water as it evaporated (because thats what the tek said), but there were none. Even at the end it was just a thickening puddle of goo.
The end result, however, is quite beautiful even with no crystals!
It seems very stable, which was the goal.
Thanks for your advice amor-fati, much appreciated!
Pokey the Grateful