Black and White and Colour chemistry from a home darkroom can usually be put down the drain as long as the Fixer or Bleach-Fix (Blix) has been de-silvered.
I worked in the Precious metal industry and we collected chemistry from Commercial labs, I also liaised with various water boards in the UK to get labs discharge licenses as we fitted silvery recovery units. The discharge levels here in the UK were similar to the US etc. It's about the load on sewage treatment works, the more spread out and dilute the better. It be unusual if a lab couldn't get a license, a large lab very close to a small sewage works was the example I was given by Thames Water Board who supply and treat London water and sewage.
At work we had a license to dispose of a few thousand litres of developer, fixer, bleach fix etc, a day but we had large plating units to recover all the silver.
You can treat your fixer or bleach fix by adding wire wool which will drop the silver out of solution, keep the sludge and then dispose of the clear solution. This will take the Silver content below the legal maximum level which is usually 5ppm (parts per million).
Ian