Pour the milk into a crock pot. Heat on low, checking the temperature periodically until it reaches 180 degrees. This takes a while (6-8 hours). You can also heat on high for about 3-4 hours.
Once the milk reaches temperature, turn off the crock pot and allow the milk to cool to about 100 degrees
After the milk has cooled, remove 1-2 cups of the warm milk and add the live culture yogurt to the removed milk. Mix in completely. Add the milk mixture back into the crock pot with the warm milk and mix well.
Place the warmed milk mixture in containers and place in the oven with light on. Let the yogurt sit for 10-12 hours. At this point you have regular non-fat yogurt. You can chill and eat at this point or if you prefer Greek Yogurt move on the step 5.
Place a colander in the sink and line it with a double layer of cheesecloth. Pour the yogurt in to the base of the colander. Let it drain for a minute or two.
Put the colander in a large bowl or other container to catch the whey, then place it in the refrigerator covered. Let the yogurt strain for about 8 hours.