Bring 8 cups water to a simmer; remove from the heat and add 3 tablespoons loose tea or 6 tea bags. Let steep about 4 minutes, until it's the strength you like. Strain loose tea with a fine-mesh sieve or remove the tea bags. Let cool, then transfer to a pitcher, cover and refrigerate.
Combine 8 cups cold water and 6 tablespoons loose tea or 10 tea bags in a pitcher. Cover and refrigerate 15 to 36 hours, until it's the strength you like. Strain loose tea with a fine-mesh sieve or remove the tea bags.
Combine 3/4 cup each sugar and water in a saucepan and add 1 infuser, if desired. Bring to a simmer over medium heat, stirring until the sugar dissolves, then remove from the heat and let cool. Strain the infused syrup through a fine-mesh sieve (you'll get about 1 cup).