Summarize:

Add 7 cups (1.65 liters) of water to a large pot and bring it to a boil, then remove the pot from the heat. Mix in the cup (118.29 ml) of sugar into the hot water and stir it until it's completely dissolved. Once the sugar is dissolved, add the 4 tea bags. Let the tea sit and cool until it reaches room temperature. Then take out and discard the tea bags. Pour all of the cooled sweet tea that you just made into a large, clean jar. Then pour 1 cup (236.58 ml) of the unflavored, store-bought kombucha into the jar. If there is a small kombucha scoby forming in the store-bought kombucha bottle, make sure that you add it to the jar as well. If you do have a small scoby in the jar, it will grow from a "baby" scoby to a larger "mother" scoby. Don't worry if you don't have a small scoby in the bottle; a scoby will still develop in your jar.
Bring water to a boil. Add sugar and the tea bags to the water. Let the tea cool. Combine the tea and bottled kombucha.