Hi Zero. As long as you buy an untreated, unbleached 100% cotton, it doesn't matter if you use cotton balls, make up removal pads or even take apart a q-tip. If you want to add a small amount to try there's some here - not the cheapest, but easy to work with :
Cotton Pad (5 pcs) - White Fog Ltd - E-Cigarette Shop UK - Best E-Cig
Cotton works best in things like taifuns, kayfuns and any vertical wick set-up (like an aga, iatty or similar), I also use it in Vivi novas
I has a bit of leakage with one of my FT juice orders too mate. But it was only about half a mil from a 50ml bottle, so wasn't too bad - the parcel smelled lovely though
You do need to let it sit for a while mate. Also if you use just a little bit too much cotton, it swells up and chokes off the wicking to the coil. It's a fine balance between superb and bloody awful. That's why I use the make up pads mate, cos I know when I cut them to size, they will be the right size if you know what I mean.
Have you got enough room to get a syringe down the side of the wick for filling Terry.
When I fill the aga, I tend to take out two of the spare screws and fill through one of the holes, that way I don't get an airlock. Then put both screws back in, when it's filled up. In fact, sometimes I vape it with one screw completely out, especially with thicker juice (50/50), just got to remember to keep the tank upright. If you don't have a spare screw in the iAtty to take out, try tilting it but have the filling point facing upwards and fill it very slowly, taking the syringe out every few seconds to release any pressure. I'm not sure what the iAtty fill system looks like, but I'd try one of these suggestions first mate.