The videos I'm seeing look like it's more trouble than it's worth to refill the cartridges. My cartridges are filled with a poly fill(I liken it to the filling you find at the store for pillows or whatever), do you really have to refill them through the mouthpiece hole? Couldn't you just go through the bottom of the cartridge where the hole is bigger? Please help! I'm about to order some e-juice and don't want to use prefilled carts. I'm using too many!