Here is the full list of all 6 The Janitor achievements.
Find the the first exit of the catacombs.
Find the second exit in the catacombs.
Collect all parts and tools in the asylum.
Find the easteregg dedicated to Ramona Lantermann, a story artist of the game.
Find the easteregg dedicated to Marcus Lantermann, a story artist of the game.
Find the easteregg dedicated to Archmeton, a story artist of the game.