I have this happen with the CE4(? stardust) clearos. It's condensation of the vapor that slowly accumulates and has nowhere to go. It's a prblem with the top coil since you tend to have to hold it horizontally of tilted so that juice tends to run into your mouth. I'm guessing since the T3 is bottom coil, most people are keeping it tilted up and not having this problem. Also the vapor travels further and cools off more in the T3, meaning more vapor will condense before you get it in your mouth.
I have a few things I've tried in general with the stardusts, but I often have to roll a piece of paper towel into a point and dry off the mouthpiece to avoid licking juice.
1. I try to release the button and pull vapor to clear it and not leave vapor in the head. If you look into the mouthpiece after you vape and see it's filled with vapor, all that vapor will condense and eventually try to go into your mouth or leak onto your PV.
2. I've experimented with cutting a small piece of paper towel rolling it up and inserting it into the mouthpiece when I fill the clearo. I haven't gotten a T3 yet, so I don't know if it can be done as easily, but with the stardust I cut a piece about 1.25" long and .75" high, roll it around something so it's like a tube, and insert it into the mouthpiece. This way the paper towel soaks up the condensation. Generally these things last for the duration of the tank. The problem is if they can't keep up then you have to fish the thing out and wipe down the inside, which can be a PITA when you're out and about.