i use a local waste hauler, and have been for about 5 years ...
besides having a 15 gallon drum, i also have a iron core trickle tank for
wash water. i too am on septic and i too worry about my "stuff" going into
the nearby stream and then into the cove. we have a delicate ecosystem
here, not just trees, lots of other stuff. the guy i use fills out the paper
work for me and charges me about $100 to take the fluid away. he hasn't
exchanged my tank yet ....
in the olde days ( read: a few years ago ) i would get a check from my
silver, now there is no check, but at least i don't need to worry about
nasty stuff in the ground because of me ...
they have drop off places near to me, but like bethe said, it isn't open all the
time, and i am pretty much excluded because it is more than just a
hobby ...
you might find out at a local lab what they do, or see if your local photo
supply store takes in spent chemistry ... i know before i mentioned to a
BIG photofinisher/portrait house that i was more than just a hobbiest, they
were gonna let me bring my stuff down and they would take care of it for
me, and in places like chicago some of the stores used to let people bring
their chemistry back to them used --- or at least they used to ...
you might also check out
http://www.itronics.com/
they purify and convert spent chemistry into fertilizer.
i originally wanted to send them my stuff, but nevada is a long way away
from ri, and they don't have a local presence yet ...
good luck!
john