Another way to precipitate the silver out of the fixer is to toss in a few pieces of loosely crumpled aluminum foil. I keep a plastic tub set aside just for stripping silver fom my fixer before re-using it (the fixer) in less-than-critical fixing jobs.(posted 8133 days ago)I read about this a few years ago in the German magazine Photo & Labor (too bad it's defunct, it was an excellent source of B&W information). Based on that article, I submitted a question to Chapman at Darkroom Techniques, who, basically said that re-use of the fixer is possible if you're willing to accept the hardening effect of the aluminum ion in the fixer.
Sooooo..... I add enough aluminum foil to assure a few bits are left after it's had a chance to precipitate all of the silver. It takes a couple of days for the action to settle down enough that I can siphon off the clear fixer. I verify that the silver content is zero, using Kodak silver test papers. I then add acetic acid to bring the Ph to 5.5, or lower, and mix it 50-50 with new fixer. After one or two "rounds", I strip the fixer one last time with the aluminum foil before dumping it.
The bottom of my tub has 2 or 3 inches of black silver sludge, which I haven't gotten around to weighing or cashing in for a trip to Reno. I really don't care about getting rich off of the silver, but it's nice to know that I'm doing my part in controlling pollution, not to mention the savings from re-using the fixer.