The TFV4 is a finicky RBA to build on. It took me many frustrating tries of leaking then dryhitting after a few vapes then finally shelved them before I threw it against the wall. I came across a method that has worked in my builds using RAYON wicking. Should work for cotton also with wide diameter coils.
-Build your coil and install. I don't use the base until after all said and done
-run the wicking through, cotton has to be just fit in the coil. Rayon has to be super tight in the coil
--problem...massive thick tails especially with rayon and not enough room in the RBA to accommodate all the tail. Try to pack all the tail and you get choking thus dryhits.
-with sharp tweezers brush through the tail removing bulk but not disturb the wick inside the coil, about 1/3 or more of the tail bulk. After doing it a few times you'll figure out how much to remove. Don't make the tails too short or you might have the top of the end wrap exposed, longer tail you can pull it back to the coil to be sure no exposed wrap.
-juice the wick and straighten out all the fibers and make a point with the end of the tail(maybe cut some excess if the point is too bulky)
-stick the point into the well, don't worry about wick sticking out the bottom just be sure no threads are catching when screwing the chimney in place.
- from the inside lift the wicking up a bit so it just sits inside the well enough to see the well full of wicking but not sticking out and not packed in tight. If lifted too much use tweezers and pull it back down and start again.
The trick is not to have too much tails causing choking of juice flow thus thinning the bulk out of the tail nor having the wicking sit on top the well. I watch many vids of many ways and they all failed with leaking and dryhits. I still have problems with the TFV4 dual RBA so I don't use it.
I've been rebuilding over 4 years now, cutting bulk out with scissors and just within the last several months I came across a vid of some guy building a coil then he thinned out the tails with pointy tweezers. I applied that to my builds in my subtank mini, kayfun, merlin and TFV4 and OMG success with better vape quality with all my builds.
I hope my explanation on wicking my TFV4 isn't too confusing to figure out cause I hated setting it all up just to leak right away or produce a dryhit after just a few vapes and having to syringe the juice out just to try again.