Hi Kevin, welcome to APUG.
I'm assuming you are speaking of the sort of quantities that a small 1 or 2 person darkroom generates.
Wetting agent is essentially detergent, so as long as you are speaking of working solution, it is fine to discard used wetting agent down the drain.
As far as silver recovery units are concerned, John Nanian (jnanian) is a long time, respected member of APUG who, among other things, markets a "Silver Magnet" silver recovery device.
John is great to deal with, and a really creative and generous photographer.
Here is his thread relating to the Silver Magnet: http://www.apug.org/forums/forum146/...ry-device.html