Hi,
    Regarding xylene usage, one should always remember that a chemical
becomes diluted with the previous chemical after every use. There is a
carryover of about 100 ml (in many cases more, depending on the
processor and how many tissues are in the retort) of solution from one
step to the next. Most staining and sectioning problems can be linked to
this. I do agree that one should be as conservative as possible with the
hazardous chemicals. That is the ecological and economical responsible
thing to do. However, it must be stressed that in many cases a patient's
very life is in that retort, so you don't want to gamble with such a
simple thing to fix.
    As a rule I always start a processor with fresh reagents in the last
group of chemicals. Rotate the rest as you want, but the last chemical,
at least, should be as fresh as possible.
Amos Brooks