Thanks a lot for all these replies!
Note to all fellow home brewers: In my area they don't sell 37% formalin to ordinary people, 20% formalin is the highest concentration you get. So based on the infos I received here, my formulation will be:
1 l distilled water
5 ml Ilford Ilfotol (can be replaced by equivalent quantity of other suitable wetting agent like Photo Flo 200)
20 ml formalin 20% solution
I will report in a few weeks whether it destroyed my film and will report in 10-20 years whether it stabilized the dyes properly