I might not be too bright, but at least I don't give up easy. Behold the implements of destruction for the next assault on the problem of the reusable highlighter. In this episode, our hero attempts to reload a Bic Brite Liner liquid-filled highligher using Noodler's Firefly ink. Here's a picture of the firefly ink in natural light. Since I don't have an eyedropper, I poured some into a Nalgene bottle with a squeeze top. Be prepared to have your fingers highlighted during this process.
Right, lets get down to business. Do not take the back end off the highlighter (the bit the pliers are pointing to.) The barrel is sealed inside, so if you try to pour ink in from that end, you'll just get ink on yourself. Trust me on this one.
Instead, take the front end off. Not the felt bit--which, incidentally, pops out easily enough but doesn't give you enough of a hole through which to pour ink--but the housing around the felt bit. Use your pliers to grasp the yellow plastic just behind the felt. If you turn it a little, it will rotate inside the barrel. So rotate it back and forth and pull on it. Eventually, you can work it out of the barrel.
So, is it worth it? Honestly, probably not. It's kind of a pain. I may keep doing it just because throwing away the empty highlighter after only a week or two of use offends my rather peculiar sense of aesthetics, but for most people it'd more trouble than it's worth. On the other hand, if someone would make a nice felt nib for a cheap fountain pen with a converter, that'd simplify the whole process quite a bit.