I've always maintained that the most important step in setting up a cartotank is the proper filling of the cartomizer, before putting it into the tank. How well you do this will determine how well that carto will perform for the rest of its life in the tank. Take your time and do it right. Your time and patience will be rewarded.
I really believe that most people new to cartotanks fail to do this correctly and do not use enough
e-liquid. Using only 15 - 20 drops in a standard carto may very well not be enough. Only 20 -25 may not be enough for an XL carto. I actually do not count drops myself. How compact/dense the filler material is may affect the carto's liquid capacity. Different types of
juice droppers may create different size drops to throw off the quantity of juice actually delivered.
I judge how much juice is enough by observation of the appearance of the filler in the carto. I add juice to saturate the carto. Then I flick the carto hard like a thermometer. Then I add some more liquid to saturate the filler. Flick it again. This two-step method is repeated until the filler will accept no more
e-liquid. The filler will have the appearance of a slushy drink -- completely saturated yet with no pooling of juice on top of the filler.
CARTOTANK SETUP GUIDE
There are many proven methods to fill a carto. One is not necessarily better than another. The best method is the one that works best for you. Condom method, drip & flick, injecting the filler with a long needled syringe, or fiddling with your thingy will all work if you learn to master it. There may be some trial & error involved. It's not uncommon to waste a few of your first cartos in a cartotank before you learn the artform.