Its been almost 2 weeks since I had my billow and the only time it leaked is when I'm refilling due to pressure. I now top fill, take the top off, juice it up, then I put the top cap on and screw it on very little, then turn it up side down then screw it all the way, then I take long hits 3 times then no leak from refilling. I don't think I'm going to need any plumbers tape or anything.
If you own a box mod, you'll notice it like us.