there is a plastic bag included with every magnet sold, it has an address on it and is a refiner
who weighs out the silver and gives users about 90% of the spot price * the weight of the silver on the cathode.
in canada there is also a refiner and in the uk that both work with magnet-users ( and i am sure anyone else who has silver to sell )
the thing that makes the magnet easy is that it isn't just a sludge mixed with other stuff, but its silver that is electroplated onto
a cathode, so it is pretty pure ... if you look in the business listings / yellow pages near where you live under electroplaters
or refiners, you might find a place near you that would be interested in the extracted silver from your fixer ... you won't get rich
but after a while it might pay for a few boxes of paper or rolls of film or maybe gas for your car ...
good to hear you have a "waste-plan"
have a nice new year !