that's it! or slotted adapter on the 901 side to bring the juice in and lower the amount left in the tank. the 510-901 adapter, at least the heavens-gift (HG09010510) adapters work fine but because of the placement of the air holes they still leave a fair amount of juice in the tank. the hole in the middle of the adapter would only save a couple mm of the juice level in the tank, and making native 510 adapters brings into question the overall length of the atomizer and whether it will fit properly in the tank at all. but using the HG 901-510 adapter, with existing slots on the 510 end, and maybe slightly deeper slots (to account for the 901 avs threads) on the 901 end as well, would bring the juice up through the bottom, keeping the remaining juice in the tank as low as it would be with a 901 really, and still leave the air holes on the 510 side. maybe i just need sleep, but i think you got it, hope!