I totally agree with this! It can be a very challenging exercise as well to get an image from inside your mind, and translate it to a drawing or painting. If you are artistically challenged, it is even more so. It is worth it the end for a few reasons. One, I believe that drawing your tulpa certainly could qualify as a form of passive forcing, especially if you talk to your tulpa while drawing him or her. Two, you end up with nice portraits of your tulpa that work as a good visual reminder and reinforcement and, again, more passive forcing. Three you get visual references you can share with other people to give them an idea of what your tulpa looks like.
I learned things about my tulpa by drawing and painting her portraits. I had to really think about what I was seeing in my mind's eye. I discovered that Melian has a receded chin, something I had never consciously realized at first. I also realized that she has thick, dark eyebrows for a girl that are a darker color than her hair. I got a better understanding of her eye color by trying to get the portraits to look right. Her eyes are actually very dark. At first I kept trying to make them a lighter blue color and it just didn't look right. There were other things too, more subtle things that are hard to put into words. But yeah it really helped to draw and paint her portraits.
Once I had some reference drawings, I was able to find other artists to try their hand at drawing or painting her. She has now been drawn or painted over 80 times by dozens of artists.