My wife uses a cartomizer that I am not familiar with cleaning. She uses transparent bottom coil clearomizers recently and likes them. They look like the picture below, with no filler.

She vapes fairly heavily throughout the day and recently the taste has lost its luster and I can see buildup on her coil. What is the best way to clean this type of cartomizer?
Thanks

She vapes fairly heavily throughout the day and recently the taste has lost its luster and I can see buildup on her coil. What is the best way to clean this type of cartomizer?
Thanks