How are you finding your Lemo`s ? with mine i had to get the air flow just right, or it seemed to flood a lot. I think i was over filling it as well. when upside down, i was filling right to the top, and i think i was having issues because of that as well.
You should always leave a little bit of air in the tank, that applies to all tanks so that when you tip it back to normal you have a bubble at the top forming the vacuum seal