In the thrilling days of yesteryear, processor failures, i.e., technician
errors most likely, were quite common.  Removal of the paraffin is key, but
you don't need to do that in a vacuum.  A couple or three changes of clean
moving xylene should do it, then backwards through absolute alcohol.  You
really shouldn't have to reverse much farther than 95% if your tissue has
been adequately fixed.  I agree with Fred that you shouldn't run it through
the purge cycle on the processor - a good old fashioned stir plate will
work just fine.  You just have to be patient.  It's better to use a whole
day to back up the tissues than try to rush to get them out the same day as
your failure.  You will only compound the damage by rushing.    This hasn't
happened to me in a long time, but (a lot of you guys will hate this) I
used to be able to tell how far to back up the tissue by smell.  If they
smelled like alco!  hol, they didn't make it through xylene properly.  If
they smelled like xylene, the paraffin infiltration was bad.  If they
smelled like formalin - they had to be backed up to alcohol.  The nose
knows.  

Jacqueline M. O'Connor HT(ASCP)
 Abbott Laboratories
 Global Pharmaceutical Research and Development
 Discovery Chemotheraputics
 847.938.4919
 Fax 847.938.3266