Not hard at all. You must be referring to a clearo tank which isnt a really a true tank in the strictest sense of the word.
I use single coil 2 hole pre-punched xl cartos from Smoktek.com and a Phiniac tank and my 10/90 and 100 percent vg juices all do wonderfully in it.
That being said if you are referring to a clearo, a lot of people have reported flavor loss and wicking issues especially with a ViVi Nova and high vg juices.
The Protank whis is also a clearo tank has the heads on the bottom and doesnt suffer from the same wicking issues and loss of flavor.