umm believe all tanks that use the kanger coil head are bottom filled. Understand it is such a pain to unscrew a atty from a battery just to fill it. I believe the Aspire BDC is a top filled tank, and I blows the kanger out of the water. Though it uses a different head.
My rba's all fill from the top, but I always remove them from the mod because it's easier to fill that way, and don't want to spill any juice on my mod's.
Aspire BDC is a bottom fill tank, that separates into 4 pieces for cleaning. Do not believe you can unscrew the top and fill, cause of the way the tube "press fits" into the atomizer.
I have actually been thinking of tapping a small hole in the top part, threading it, and finding a small thread thumbscrew to seal the new hole with. When filling the Aspire from the bottom, it always leaves what seems like quite a bit of empty room at the top (because of the length of the coil package). I have a nice tap & die set, but no material, nor a way to make a knurled handle on a screw.
Otherwise, I love my Aspire BDC so far (about 3 weeks).