It's Always Sunny in Philadelphia: Season 12, Episode 2

12 - 2: The Gang Goes to a Water Park

The gang takes a trip to a local waterpark, ripe with personal agendas and ulterior motives. Dennis feeds off his mantra of "the park provides" and takes on a protégé. Frank and Charlie are determined to ride every ride by any means necessary and Mac and Dee get stuck in a tube slide for most of the day.