In an example of the disclosure, service rotation of a drum along a longitudinal axis of the drum is caused. The service rotation is to apply a centrifugal force upon a liquid held by the drum. The centrifugal force pushes gas bubbles in the drum away from a curved surface of the drum and towards the longitudinal drum axis. The gas bubbles evacuate from the drum via an outlet tube positioned adjacent to the longitudinal drum axis. A production rotation of the drum is caused after the service rotation.