I've just got the kanger e smart cigarette and it's my first e-cig. This has a clearomizer and I wanted to know how do I clean it since your not supposed to get any liquid in the middle tube and how long do they last before i would need a replacement. Would I be able to use it until it stopped working or is it advisable to get a new one after a certain amount of refills? How long does a clearomizer last?