In large scale silver recovery silver is plated out of recirculating fixer or bleach fix (blix) using sophisticated plating units that control the ampage precisely, too much current and the fixer is destroyed.
On a smaller scale usually mixing the bleach fix (prints) with the fixer from films after colour processing and also the rinse/wash water is sufficient before passing the solutions through a device like the Silver Magnet units. This will remove most of the silver however the remainder should be removed by then passing the solutions through a Steel/Wire wool cartridge.
The Silver magnet should reduce the level of Silver to 10-15 ppm (very approx) with the cartridge as well to below 1ppm. With just a Silver Magnet then the spent solutions should be diluted by about 10 -20X to comply with the legal 1ppm discharge limits (most areas UK/EU/US).
Black & White processing:
With B&W fixer the Silver Magnet will work more efficiently even with undiluted fixer - which it's designed for.
It needs to be remembered that the small volumes used in home darkrooms are normally very heavily diluted by domestic water wastes and are of little or no concern to waste authorities, but you need to be aware of local regulations.
Kodak's guidelines for safe disposal of photo chemistry are based on agreed procedures accepted by virtually all authorities in North America and The EU/UK and are available online.