To all of those "disposing" and "neutralizing" their used formalin, I
have but three words:
RECYCLE, RECYCLE, RECYCLE!
Recycling our used formalin saves us over $9000./year in disposal and
repurchase cost.  We have never had a quality issue with our recycled
formalin and CAP, state and federal inspectors are always impressed.
The only formalin waste being disposed of in our lab is the 1% or so
formalin waste that comes off the recycler after a run.  We recently
started neutralizing that small amount (5 or so gallons/week), and
lowered our disposal cost ~70%.  You should keep detailed records of
what you do to the formalin and how much of that product you introduce
into the sewer system.
Bob Santoianni
Emory University Hospital
Atlanta, Georgia