Prefilter funnel?

I'm ready to convert my fina, and the only thing I'm missing is a funnel for pre-filtering. I have no idea what kind of funnel to use, but I can see that too big of a funnel is going to stick into the vial, and too small a funnel won't even work for the pre-filter. I don't want to screw up and spill any of the good stuff, so does anyone have any quick ideas? I thought about using a make-shift funnel, but I don't want to take any chances of making conversion errors.

I got a small one from an auto store and washed it really really good. It was like 1-2 dollars.

Pain