How long have you been using that particular cartomizer in the tank?
There's a few things that can cause flooding of the cartomizer.
First of all, allowing e-liquid to enter into the center air tube when filling from the top of the cartomizer, or if filling it via the condom method not blowing the excess e-liquid out of the tube before putting the cartomizer in the tank. If filling from the top, placing a broken wood toothpick into the air hole will keep e-liquid from getting in there.
If you are filling the tank with the top cap off, placing the cap on the tank will force too much juice into the cartomizer and lead to flooding. The best technique is to fill the tank through the top cap's center hole with the cartomizer only 1/2 of the way into the tank. (see video demo in my blog) Again, be sure not to allow juice to enter the cartomizer's air tube when filling the tank.
Vaping technique: Pulling too hard can force too much liquid into the cartomizer resulting in flooding. Gentle, patient, 3 - 6 second draws work best. Imagine sucking on a straw in a milkshake.
After a few days of use, some cartomizers will just flood on their own. The fluid/air barrier within the carto just breaks down and juice enters into the air tube. This may happen more frequently with poor quality cartomizers.
I believe you have already visited my blog articles (I remember you leaving a positive comment - thanks). For others who may be reading this thread having similar flooding or leaking issues, I have a blog with articles on cartomizers and cartotanks. The one on cartotank setup has a link to a video done by PBusardo via You Tube on cartotanks and troubleshooting issues you may have with cartotanks.
You can find these blog articles by clicking the link under my avatar.