Tank, are also called Clearomizers because they are typically a clear looking tank with an atomizer inside. Atomizer is the core of the device that converts e-juice into vapor. There are usually two main types of atomizers, top-coil atomizer where vapor is produced mid- or towards top of the tank, and bottom-coil atomizer where vapor is produced at the bottom of the tank. A typical 1.6 mL to 2 mL clearomizer tank lasts about 1.5 packs to 2-packs worth. Larger tanks last longer per refill. A dual-coil atomizer produces more vapor than single-coil atomizer.