For new carts/same flavor I bought a little needle-tipped bottle (precision oiler is another name for it) on the suggestion of another poster. A syringe also works great. Then you want to stick the needle part through the foam liner to the bottom and fill with liquid til it's slightly wet at the top of the liner, but not heavily pooled either.
Not "through" the filler, but down along the side of the filler against the cartridge edge. If you try to go down through the filler you will push the filler down, which means you'll have to pull it up again afterwards.
Now, having said that, I have learned something that I had not heard before, and maybe it is just me being lame or something, but I am pretty certain at this point that this is solid knowledge within my brain now.
I finally ran out of blank cartridges, and started refilling them for the first time ever. They do NOT work nearly as well as the first time I filled them. I have been struggling with them for a few days now, and tasting a lot of that plastic burning taste from lack of juice flowing to the atomizer.
Everytime I look at the cartridge to see what is up, the damn filler is pushed down from the top of the cartridge. It is not in good solid contact with the atomizer. I have to keep pulling it up or topping it off to get some vapor flowing. But everytime I pull it up, it soon fails again, and I open it up to find it has been pushed back down again.
I tired of this finally, and decided to clean one of my fillers before trying to reuse it. Works like a freaking charm. I just pulled it out, rinsed it in the sink, and smashed it flat in a paper towel to get all the water out. Then it is all fluffy and happy and fills the cartridge up all nice and puffy. And it works like new.
So did I just stumble on to the holy grail of refilling cartridges, or am I somehow totally lame?
I haven't heard anybody talk about refilling their cartridges and having to do anything to plump them up again other than just refilling them and moving on happily with their lives. But I can tell you right now, without doing this, all of my cartridges that I've tried to refill are shrunken, need to get pulled up, and get pushed downwards everytime I reconnect them.
So although I've never heard anybody say it before, I strongly recommend cleaning out your cartridge filler before reusing it even once. As for me, I placed an order for 50 blank cartridges for only $12.00 at Heaven Gifts (Ruyan) and I will never again refill without cleaning them first. But if I can keep on getting them for 24 cents I may never even bother with that.
Damn, I may have to start using that bag of polyfill I bought to restuff them myself at some point, as much as I loathe the idea. But I keep on hearing how people just refill them two or three times (at least) and I've never really heard anyone say they have to mess with them like I have to.
Anyway, take it for whatever you think it's worth.