Roman, here is what I remember of my most recent experiences trying to develop colour slide film to give a B&W positive.

Like Kate, I had come into a bunch of colour slide film for cheap and didn't particularly want or need a colour image. In experimenting in trying to get B&W positives from this stuff I first used the method of Mikhail Garous provided in the link Alessandro gave. I tried it with this Fuji MS100/1000 according to his directions and got very dark positives (deep-brown-and-white rather than black-and-white -- I used a reasonably alkaline thiourea toner bath). Unfortunately, the highlights were still quite 'dense' despite prolonged bleaching and no matter what I did, including overexposing by several stops, I could never get rid of the highlight 'veil'. My conclusion was that the thiourea toner had reacted somewhat with developed silver grains as well as with the left-over silver halide, meaning that even after bleaching I couldn't get clear highlights no matter how hard I tried.

I never tried the tin chloride version but it may work better.

In later experiments I tried developing a roll of colour slide film in a traditional B&W reversal process. Under conditions that gave pretty good results with Pan F Plus, the slide film totally disintegrated -- the emulsion came completely off the film base. I was as surprised as Roman is, since slide film is made to take a beating. It could be that more gentle bleaching would accomplish the bleach step without destroying the film.

Preserving the order of Mikhail Garous' method (develop, tone, bleach) using B&W reversal bleach based on dichromate or permanganate does not work, as these bleaches also destroy the 'toned' positive. I found this out the hard way as well.