You may have one of those great jars that has the spigot on the bottom-there are everywhere right now. I have an old pickle jar my Mom gave me a while ago and it suits me just fine. It's about a gallon in volume. Once I make the tea, I pour it into two smaller pitchers that fit in my fridge. If you are using a spigot-equiped jar, leave a bit of space at the top.
For this amount, I find 12 tea bags--regular ol' orange and black cut pekoe works fine. You don't need the cold-brew ones either because the sun is going to heat this up. Just dunk them into the top and screw on the lid and leave your jar out in a sunny spot. The longer you leave it, the better the tea. I leave mine out for about 6 hours. Nice and dark.
When the tea is brewed, remove the tea bags. In a small saucepan, combine 2 cups of sugar with 1 1/2 cups of water, stirring until the sugar is dissolved. Boil for one minute; this is called a simple syrup. This is the best way to sweeten your tea because it ensures you won't have sugar sludge on the bottom of your jar in the end. It's also better because it takes twice as much sugar to sweeten a cold liquid as a hot one (* that a bit of science for you, kids). Stir in your syrup and add 1/4 cup (or more if you'd like) of lemon juice to the tea. Top off with ice and chill.
Miss you, Gram.