Clearomisers differs from e.g. cartomisers by not having filling (like a filter on a cigaret), but instead having one ore more wicks that draw liquid to the coil / atomiser head (evapotator).
The tanks are available with both top and bottom coil. Top coils have wicks at the top of the container which feeds the coil. Bottom coils (BC) have wick and coil in the bottom, which in many cases are better 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 provides thicker vapor than single coils, because there are two coils working at the same time.
All kinds are known for their pure taste, good vapor and being easy to fill.
The tanks come in transparent, colored and even with covers, giving them a little more cocky look.
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 miser from the battery and give a gentle blow into the mouthpiece. When you are done make sure to wipe of the threading on the miser before replacing it on your battery.
Many tanks are like the majority of clearomisers 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 suspekt a liquid or just want to be safe, you should use a tank made of glass (Pyrex).