Jill, we have been using zinc formalin for years now.  It is wonderful for 
the immunos in that it gave us consistency in staining, especially the 
difficult ones, such as ER and PR.  We have also replaced our B-5 with the 
zinc formalin.  All our bone marrows and lymph nodes are fixed in it.  We 
have it in all our specimen jars and in both processors.  The zinc formalin 
can rust metal lids on specimen jars and formalin pigments are present in the 
sections.  It has not hurt the processor since we do a hot water flush often. 
 We get concentrated zinc formalin from Anatech.  
Hope this helps,    pearl