>>7600904
every single sharpie and fineliner is refilable: inside is a plastic tube filled with foam and that foam is soaked with ink. the tube is connected to the tip and ink flows to the paper via capilary action. the only struggle is how to open the pen without destroying it: some brands have easy to pull out endings, where all you need is pliers. some brands seal off the end with plastic so well that you cannot getbinside without sawing the other off.

pic related: test it out yourself on your depleted fileliners and take it apart. simply dip the tube with a foam into any bottle of ink, let it soak the ink and then assemble sharpie back. it will write just as new. as to which kind of ink to use, i would recc sticking to the ordinary water based. but alcohol ink (permanent marker) or even the pigmented ink should work as well. you need to be brave and experiment a bit. if the ink wont flow well, add some water to the tube in sink to make it more drippy.

some brand are even made with being refillable in mind: they have screwable body, so you dont even need pliers to pull them off and come with extra tips to replace.