There are plenty of sun tea recipes around, including a couple on Instructables, but I have a different method that cuts out the middleman.
Buy a plastic half-gallon beverage jug (oh, this is Instructables, so go collect some old plastic bags and make one). Clearish is preferable.
Buy a box of Red Rose black tea. It costs more but tastes better than anything else you can get in the US (unless you like *ugh* flavored ice tea*). The Canadian variety of Red Rose is supposedly even better. And there's a prize in every box.
(*yes, I did grow up in the Deep South, where we drank ice tea, never "iced" tea).
Step 1: Tie One On
Fill your container with fresh tap water.
Take 5 standard size Red Rose tea bags, sort them with the tabs at one end, and tie an overhand knot in the strings.
Place bags in the water filled container and put the lid on. I like to tuck the logo tabs outside the container to keep things neat and make it easy to grab the bags for tossing into my compost bucket.