For the FBs, whenever I was sloppy filling (injecting air even when filling properly upside down) I would get some dry hits. I was able to remedy by reinserting the needle with the FB upright (drip tip up) into any airspace and very slowly and carefully sucking a small amount of air out to try strengthen/reestablish the vacuum/pressure inside. As I drew air out, a couple small bubbles would float up from the wicks telling me I had reached some form of pressure equilibrium...