This depends on whether you have the newer model or older model. No matter which model you have, you must first wrap Teflon tape around the top of the metal threads on your machine 15 times to ensure a good seal.
1) Newer model – The newer model has a separate plastic piece that screws onto the metal threads. After taping the metal threads, screw the plastic tower connector to the metal threads until they’re finger tight. From there, place the black o-ring onto the connector so that it nests between the tower connector and the main tower piece. To secure the tower, turn the sleeve at the base of the tower to screw it into the tower connector.
2) Older model – This tower originally had no connector and instead screwed directly onto the metal threads. After taping the metal threads, screw the tower on until it’s finger tight.