Roxy, I top fill my Orchid my removing the top and holding my fingers over the holes and such. Works great. But with the Billow, sometimes the chimney likes to spin and come with it since it is threaded onto the top cap. Even when I tighten the crap out of the chimey onto the base, it usually will still come loose before it does on the top cap. So it doesn't really work that well like the Orchid does.
Personally, I like the chimney to break loose from the deck when taking the top off. Then I can invert with a full tank of juice and remove the top and chimney, take out the drip tip, and set it down while I change wicks or dry burn. One of the reasons I love the Billow in fact is that threaded top cap to chimney. No more draining a tank to re wick or set new coils or what have ya!
Yeah, top filling the billow is more difficult