WHO NEEDS AIR?
Suffocate for 5 continuous minutes without dying
Borderlands The Pre-Sequel WHO NEEDS AIR? – Achievement / Trophy Guide
This cannot be done with Claptrap.
Go to Moxxi’s Bar and buy the SQUILL SYRUP for 10 Moonstones. You get these as drops from enemies. Once you have it, your health will be restored outside and you can survive up to 30 minutes. You only need 5, so you just have to step outside and wait for the achievement/trophy to pop.