Casco EZ Aqua UV bulb help for comet system

My store has the Casco ez aqua system. I’ve changed the UV bulbs in every section except the comet one. The plumbing is different because of the automatic water change feature. In the video PetSmart shows a guide to change the UV bulbs the author did not mention how to change this one. I’m assuming I do it the same way minus disconnecting the plumbing but I’m worried all the water in the tube above it will drain out. Anyone able to help?