Before you have to restuff I have found that recycling them goes a quite a long way. This has worked so well for me i will post a little guide on how I do it.
This process works so well for me I just had to share. I can recycle my cartridges and they work like new I've done it 3 times already with all my cartridges.
Step 1:
Take the cartridges you got pre-filled or ones you filled yourself.
Step 2:
Using normal tweezers gently pull the white filling from your cartridge. Notice they are brown from the residue e-liquid
Step 3:
Drop them in a sink or bowl filled with just tap water at room temperature.
It should take only 1-2 minutes for the brown fillings to turn white by themselves.
Step 4:
Gently take the fillings from the sink and place in paper towel. you can let them dry on their own(Not in direct hot sunlight). You can speed up this process by VERY gently pressing the fillings against the paper towel then let them dry thoroughly.
Step 5:
Use a Q-tip to clean the shell of the cartridge. Careful not to push too hard or you can move the plastic plate at the end of the mouthpiece.
Step 6:
Using the tweezers now with the dry clean filling insert it back in the shell.
Step 7:
Done! you have an almost brand new cartridge ready to be filled with any flavor.
IMPORTANT!:
If after you refill and start vaping you feel the e-liquid is seeping through the back plastic plate in your mouth STOP USING IT. Myself and a friend learned the hard way that if you taste the liquid and keep tasting it you can get a horrible queasy nauseated feeling. It goes away after an hour or two but it terrible while it lasts.