IGN’s Carrion guide has collectible locations for every hidden item in Carrion. In this game there are nine containment units, and each gives you a special ability to help you progress. Some are required to finish the game.
In this guide, collectibles and containment units are the same thing, so they’re used interchangeably.
If you are going back after your initial run to finish collecting the Containment Units and finish the achievements, you can always return to the secret Communications Room/Control Room to see your gameplay status and orient yourself.
From the initial boot-up point after finishing the game, squeeze into the pipe and back into the Frontier. Go left and squeeze into the door; you’ll see each screen to assess your gameplay and progress, including which containment units you haven’t unlocked yet.