Brew the peppermint tea and let cool to at least room temperature. Mix with pineapple juice, add ice, and garnish with lemon slices.
Put all in the slow cooker or crockpot and and turn on high until hot and then turn on low or just put on low and leave it. Serve from the slow cooker or crockpot all day.
Add the above ingredients to a pitcher of water, chill and serve. Flavors will become more intense the longer it sits.