Judy,
I don’t know what you’ve seen before, but the arrangement my
employer uses seems to work. The sink drains, via a simple straight
down short pipe open at the bottom (no U trap) into a plastic trash
can. The can is covered, but the lid is perforated (and upside down
to act as a funnel) to allow liquid to drain through. Between the
sink’s drain pipe and the trash can, in that gap is a plastic tray
suspended on a wire bracket. The tray is some sort of generic office
paperwork tray, chosen because it has a solid bottom, but, after a
slight lip, the sides are a mesh. So water that drains down out of
the sink lands first in that tray. Any dropped small items (typically
stones that came loose in cleaning, etc) will be easily retrieved
from the tray, which is easily removed from it’s place under the
sink. Larger bits of metal stay there too. Most of what ends up
being recovered, the very fine stuff like polishing residues, flows
out of the tray into the trash can. The can has an outlet near the
top on the side, which then leads to the usual U trap and the sewer
line. Water with it’s carried valuable mud has time to settle out in
that trash can, so what goes out the side drain is pretty much just
water. The mud accumulates, and eventually gets collected and
refined. We have two of these systems. The one under a larger shop
sink where lots of things get washed, hands, etc, has two such trash
cans hooked up in series. Not much gets past it. This system also
allows us to rinse out things like casting investment mixing bowls
(most of the waste investment goes in an actual trash can before
going to the sink, but this way we can easily wash the bowls and
mixing tools out in the sink.) This does of course increase the bulk
of the trapped material, but it keeps the plumbing lines from being
clogged with the stuff. In the polishing room, where most of the
polishing and jewelry cleaning is done, there’s not enough room under
the small sink for a double system, so it’s just one small trash can.
Seems to work well enough. One refinement to that is that the outlet
drain, on the inside of the can, is fitted with an elbow fitting
pointing down, so water has to flow up into that drain. The opening
into that elbow is still high enough in the can, but decreases any
tendency for the water to move straight to the drain without having
time to settle out. One could, if desired, build an actual baffle
plate structure into this, but it hasn’t seemed to be needed. These
whole systems are made from simple hardware store plumbing fixtures
and Rubbermaid trash cans. Cheap and effective. The only downside is
that the system is not sealed from the air, so if you get some
fermentation or the like going on, the mud can get smelly. Avoid
washing food dishes and coffee cups in there to cut down on that. We
got some sort of industrial deodorant/disinfectant that gets added to
the tank now and then if odors become noticeable. Not sure what it
is. But I can tell you that the precious metal return from these
setups, every few years, is quite more than enough to justify the
fuss. Kind of amazing, actually…
Hope that helps
Peter