The deal is available starting June 1 and runs through August 31, 2016. It's only good for carryout at participating locations.
Pizza PepsiMoji bottles can be found wherever Pepsi is sold, while supplies last. It's limited to one free pizza per bottle (I'm guessing they'll need you to hand over the bottle). You basically need to find the Pepsi bottles with a picture of a single slice or whole pizza on it (which could be difficult depending on how popular this promotion is).
Photo via Pizza Hut.
