Do you have the small cone, or the big one? Unless something changed, the small cone won't fit with the mini tank; I have two, of each. It does fit the big cone though, as reported here.i don't know what you mean by filing down? i use the cone on my triton, you just have to put the cone on first, then put the tank in... i havn't done any filing. personally i like the look of the cone better as i use the mini tanks alot, and every one tells me the mini and triton tanks look like needles lol.. the cone gives it more of a fancy pen look.