"Refill it yourself" came from the UK
The diagram I drew in 1992 to help people disassemble their HP LaserJet II cartridge. To everyone's relief, digital cameras were invented shortly after.
First, some definitions. Sorry to be pedantic, but it's important to get this right.
The phrase "toner refill" implies there is a cartridge that has been used and is now empty. In other words, toner powder will be put back into an empty cartridge.
Now, there are only two commercial activities that have ever taken place that fit this definition.
The first might be called "professional refilling" (I use the word "professional" loosely). Also known as toner cartridge "remanufacturing". And kudos to our cousins across the Atlantic, it was the Americans that lit a rocket under this emergent industry in the late 1980s. Basically the proposition was, "Give us your empty HP toner cartridge and we'll give it back to you full again. And we might just change some of the old and sensitive components, like the OPC drum, just to make sure it reaches the end of its second life. OK?"
1996: the world is threatened by a huge HP LaserJet 5L cartridge and gigantic apple corer. Lead photo from our website just after inventing "melt and pour".
Simultaneously, "remanufacturers" were able to glean back thousands of unwanted empty cartridges from the offices of the world. They were then able to remanufacture those empties and sell them back to users as a stand-alone item. A quick surf on the interweb will show you that remanufacturing is alive and well today, often masquerading as a "Premium Brand Recycled" toner cartridge. And if you don't know what "Premium Brand" means, you're not alone.
Today, melt and pour harnesses cutting-edge technology, such as electricity
But there's another business activity that fits the definition of "toner refill". And I know a lot about it because, along with my old Dad (RIP) I invented it (in 1992). And marketed it. And invented widely copied variations of it, like the notorious "melt and pour" (in 1996). And "unplug and pour" for the Samsung ML-1210 (in 2002).
I refer to none other than the do-it-yourself toner refill. Which means you by hook or by crook, get that toner powder back into your empty toner cartridge.
A picture, they say, paints a thousand words. But a Youtube video - made by someone who's taken the trouble to actually try it themselves first - just about says it all. So check out the two videos here. 90% of all laser printer cartridges can be refilled by one of the two techniques shown. Although "melt and pour" is gaining more importance: the last printer manufacturer to use plugs in its cartridges, Brother, apparently ended that practice with the recent HL-3140CW family.