Hi Geoffm and welcome to the forum!
I started off with the eGo-C system, and yes: leaking is a very common complaint. Unfortunately, there's very little you can do to solve the problem completely but there are a couple of things you can do to improve it.
One thing that does help is to use a very soft draw. If you hit those things too hard, they wick too fast and the liquid will try to escape any way it can.
What kind of juice are you using? I found that a 70/30 PG/VG ratio worked best in the eGo-C. Thinner juices would leak like crazy and thicker juices wouldn't wick at all.
You also mentioned that you're going through 2 tanks a day. Are you replacing the caps? They're not meant to be reusable. From memory, they cost about 10p each and you would do well to replace them on a daily basis as that will help to minimize leaking.
JJ