Clearomisers differ from cartomisers by not having filling (like a filter on a cigarette), but instead having one or more wicks that draw liquid to the coil / atomiser head.
The tanks are available with both top and bottom coil. Top coils have wicks at the top of the clearomiser which feeds the coil. Bottom coils have wick and coil in the bottom, which in many cases is better at preventing burnt taste which happens when the wicks do not get enough liquid.
In addition there are also both single and dual coils (DC). Dual coils usually provide thicker vapour than single coils, because there are two coils working at the same time.
All kinds are known for their pure taste, good vapour and being easy to fill.
The tanks come in transparent, coloured and even with covers for more protection.
Never fill your clearomisers all the way to the top. And also never let them get completely dry.
You have to take care not getting liquid into the middle tube. If you do you will experience gurgling and you may get liquid into your mouth. Should this happen, then remove the atomiser from the battery and give a gentle blow into the mouthpiece. When you are done make sure to wipe of the threading on the atomiser before replacing it on your battery.
Many tanks are like the majority of clearomisers are made out of polycarbonate, and therefore some liquids should be used with care or not at all.
There are numerous liquids available and Pink Mule offers no warranty on tanks ruined by these. See some examples on liquidshere.
If you suspect a liquid or just want to be safe, you should use a tank made of glass (Pyrex).