After draining the ink, proceed through the newly accessible areas. You'll eventually find yourself in a large, open area where Sammy Lawrence will appear. He's a tall, ink-covered figure wearing a Bendy mask. He will capture you and tie you to a pole, intending to sacrifice you to Bendy.
During this sequence, Sammy will deliver a monologue, revealing his twisted devotion to Bendy. You are helpless during this part. Eventually, Bendy himself will appear and, instead of accepting the sacrifice, will attack Sammy. This provides you with an opportunity to escape. After Bendy dispatches Sammy, the ropes binding you will loosen. Interact with them to free yourself. Grab the axe that Sammy dropped nearby. This axe will be your primary weapon for the remainder of the chapter and is crucial for dealing with the Searchers and other ink creatures you'll encounter. Be prepared for a brief chase after you free yourself, as Bendy might still be in the vicinity.