I am afraid you’d better do not clean it at all. I got two CE4 with my starter kit and never figured out what to do with them. I just added juice and vaped a mixture of old and new juice. To clean them you should pass through this small tube a lot of water, get wicks wet and then wait them to dry out (could take a few days in rather closed compartement, I think).
Fortunately a few days later I got my second vape mail with better clearos.
P.S. However experience was useful. Even now I often do not clean my tanks between juices and enjoy (for a day) some rather interesting combinations.