Fill a large pot with water, add soy sauce and vegetables. Bring to boil and lower heat to simmer.
In the mean time, place flour in large bowl. Add just enough water (about 1-2 cups) to form a moist, elastic dough. Knead for ten minutes.
Fill bowl with warm water to cover dough, and let dough rest for 10-15 minutes. Without removing water, begin kneading dough under the water. Water will turn milky white, and as it does so, carefully drain out water and refill. Repeat until water stays almost completely clear. For a while it will seem that the dough is just going to completely fall apart in a disgusting, gooey mess, but keep at it. All of a sudden the dough will begin to toughen and soon you'll be left with a nice, elastic ball of raw gluten. The more you knead it, the tougher it will get, so adjust to your liking.
Once you have your small, elastic ball, drain all water away and rip dough into small chunks and drop into simmering water. Simmer for one hour, occasionally stirring, as seitan pieces tend to float.
After simmering, you can store the seitan in the broth and it will keep in the fridge for quite a while. You get a ton of seitan out of this, and its pretty fun to make as well! Happy cooking!