As answered by 7Bread7, you hold the Biocell in your mouse-pointer, and hover it over a Biotank/storage; and then left-click on it to fill it up!
Apologies for the confusion, If you have any suggestions on an alternative method, do let me know!
Maybe add option to right click menu? Something like: Fill container / Fill from?
Thank you for your suggestion! I'll look into it!
