Rudy, PE, thanks again for your replies.
I use "modern" thiosulfat ammonium fixer diluted for paper (1+9), and let the print fixes for 2 minutes (for FB papers). The fact that the Fortezo heavy paper, Museum weight (280g/sq. meter !), would be easily washable, is rather counter-intuitive to me ! But I have to make further tests...
So, on advice of PE, I decided to discard the HT2 solution I made.
Maybe I will try to make cheeseparing economies here, but is there a mean to salvage the Silver nitrate in solution ? If I dilute the solution with distilled water, and let it evaporate in a crystallizing dish (possibly in darkness, not under the sun !), can I obtain silver nitrat crystals, or it is permanently destroyed by acetic acid ?