It sounds like it is flooding. Several things can cause this;
Not assembled correctly
If the head isn't screwed all the way in the
device can leak, although this is usually a "leaking all over your battery" problem, not a flooding problem.
Juice is very thin
It's impossible to make a bottom coil head that suits all juice types, though by and large bottom coil devices are fairly forgiving. You could try a thicker juice if this happens with all heads, or you could try adding another flavour wick. You'll find videos that will show you how to *remove* a flavour wick, just add instead of remove.
You could also try another head, or try heads from a different manufacturer.
Head is faulty
There's not much margin for error. If there's not enough wick in there to fill the holes then you may get leaking and flooding. Sometimes all you have to do is wash the head and fluff the wick up a little. I once had a new CE3 dump its entire contents all over my desk immediately after filling.
Try another head or fix the one you're using.
To clear a flooded bottom coil device:
Turn it upside down. Blow through it into a tissue or rag until it stops bubbling. Keep the rag over the mouthpiece and flick it to expel any juice remaining in the centre column. Wipe mouthpiece and continue vaping.
ETA:
Oh, and technically a T3 is a clearomiser, not a cartomiser. A cartomiser is a metal tube with fibre matt filling and an embedded coil, much like the cigalikes use but can also be inserted in a tank (a carto tank).
ETAA:
I'll also add another "reason". This is the one that can trip people up even when everything else is right:
Draw is too tight
Because the wick is at the bottom, negative pressure in the center column (sucking) can pull too much juice in through the wicks. The less liquid there is in the tank the more severe the problem is likely to be. Take a couple of dry pulls without firing the battery. If the head immediately floods your draw might be too tight for the head setup.
