I have a Brother MFC-290C, LC61 ink cartridges. Can't find anywhere to refill. Can you help?

I read the detailed account of how to refill the LC61 cartridges but these do not have a "small square with a dimple in it" I have drilled out so many holes and not once found a spot that had ink and yet there is some ink showing in the little window. I need a detailed picture of an LC61 ink cartridge in order to find the "dimple" on top. The front has a section that slides back and forth when it is inserted into the printer.