Rinse off the soybeans and place in a large bowl. Add enough filtered water that the beans are covered by several inches. Allow the beans to soak for 12-18 hours, or until the skins pop off easily when squeezed.
Drain the beans and place in a blender along with 6 cups water. Puree until very smooth, 2-3 minutes. Strain the liquid into a large bowl through a butter muslin, triple layer cheesecloth or nut milk bag. Make sure to squeeze out as much liquid as possible. Discard the solids (or look up other ways to use them in cooking).
Place the liquid in a large dutch oven and bring to a simmer, stirring with a rubber spatula to avoid scorching. Continue to simmer on medium-low heat for 20 minutes, stirring frequently.
Allow the soy milk to cool and then store in the refrigerator. Use within 3-4 days for best flavor.
I like to let the soy milk reduce for a thicker final product. For thinner soy milk and a greater yield, simmer over low heat.