The b&w fixer probably works but more knowledgeable people here warned me against that. I'm out of my league here. Color fixer is cheap and is ok for b&w negs and paper as well.
If you're using tetenal c41 kit, follow the instructions, just replace the blix with the fix. However I don't remember what fixing time at should be 38C. You should be able to find it on net.
I remember that BB on print was discussed here as a method of reducing contrast. I do not have any experience on that.