Thank you all for your timely responses to my question regarding disposal of Zenker's.  I should have clarified what we are using it for- we only use it for a PTAH stain, not for any processing of tissues- which brings me to part 2- can anyone recommend a PTAH stain that does not use Zenker's as a mordant?  We are a small veterinary laboratory and don't do PTAH that often.