Hi, I had exactly the same problem filling the carto tanks before. If you think about it, it's obvious - when you pop the cap on, you create air pressure that squeezes the liquid out of the bottom.
The key is not to take the cap off! Leave the carto on the battery and take off only the drip tip, then carefully slide the tank up until you have a small opening between the carto and the tank wall, just enough to fill in the liquid. Slightly angling the carto helps as well. When finished, slide the carto down again and replace drip tip. Works like a charm, every time.
Ozy gave good advice. There's multiple ways to assemble and fill a carto tank, but I've found the following tips to work best:
Fill a new punched carto that will be used in a tank the same way as you would if using it alone. Put a wooden tooth pic into the airhole while filling from the top to keep juice out of there. Fill with juice until the polyfill looks like a wet slushy drink.
Using a tank accessory tool like this will protect the o-rings in your endcaps from being damaged by the sharp top edge of the cartomizer.
View attachment 137688View attachment 137689Slap-yo-moma tank tool from Big Daddy Vapors
0-rings are the only thing that keeps your liquid from leaking between the cartomizer and the endcaps; if they are damaged the tank will eventually leak. The tool also speeds up filling the tank with juice as it prevents juice from again getting into the airhole.
The above pictured tool is more expensive than other tank tools, but having used them all the one pictured is hands down the best and worth the money. Trust me. The one tool recommended above in this thread is only useful to add juice to an assembled tank, and will not protect the o-rings during assembly.
As pointed out by Ozy, don't fill the tank with juice unless both endcaps are already on both ends of the tube. Once the tank is nearly full, push the cartomizer the rest of the way up through the top endcap, remove the accessory tool and replace it with a drip tip.
