First, get a Starbucks gift card. You get them at Starbucks and you tell the cashier how much money you want to put on it. You have to put at least 5 dollars on it.
Then, register the card online at starbucks.com
Now, when you use your card to pay, you can get free refills on iced coffee, warm coffee, and iced tea. Normally, they charge you 54 cents. But your registered Starbucks card gets you the refills for free.
Try to tip them and they will be happy to serve you as many as you want.
The most I ever drank is 7 Venti iced coffees.
The cool thing is that if you originally bought an iced coffee, you can get an iced tea for your refill. You can switch it up every time you get a refill if you want.