The Halperin Hotel is the second main region you get to explore in Dead Island 2. It's full of Caustic-X pools and military zombies, as it was an evacuation point for Bel-Air and Beverly Hills people.
It's also where you first encounter a maglock door in the game. Speaking of locks, there are also a few locked safes and stashes in Halperin Hotel. The Poolside Bio Container is one such locked item. Here's how to get the Pool Container key in Dead Island 2.
How to Get the Poolside Container Key in Dead Island 2
You can get the Pool Container key by killing a Putrefied Slobber called Sunbather. They spawn in the outer perimeter of the Halperin Hotel, where you also find Jamal from the Missing: Jamal Lost and Found quest. You can find their exact location in the screenshot below.
Once you have killed Sunbather, grab the poolside container key from their corpse, and head to the pool in the Halperin Hotel. You first visit this location during the main quest, "Room Service for Major Booker." You can find its exact location in the screenshot below.
When you come back to the pool, you will notice that the area around the Poolside Container is covered in acid and bursting slime things. Shoot the slime things with your guns before proceeding. Also, grab a water jerrycan from nearby and clean the acid from the floor.
Once you have cleared the path to the Poolside Container, unlock it to get a Superior-tier weapon.