Good point about the rubber. But they could use several o rings to make the seal.
Keep in mind, I bought 10 and have only been using 1 of them but is anyone having a problem with filling. What I mean is that when I top mine off, I literally have to lay it on it's side or the juice comes out the connector end. I'm being extremely careful that juice doesn't go down the airhole. What gives with it? I love the way they vape and the capacity but it boogles me as to the dripping out the hole when refilling this one. I guess I need to open another one and see if it does the same. I will keep buying them as I am really enjoying this one. If anyone else has experienced this, please post. I've been filling cartos for a long time so I know it isn't me just getting old....LOL.