Soil trap for sink?

[Bill Williams]

We're about to move into a new building, and we specified that our
laboratory should have a soil trap in the sink.  It's put up or shut up
time now:  the guy in charge of finishing up the building wants me to
tell him what such a trap looks like and/or where he can get one.  I
haven't the faintest idea!  I know they exist, and I've used sinks with
'em, but I never examined one in detail.  If anyone can help, I'd sure
be appreciative.  The best possible thing would be a specific reference
to a plumbing or greenhouse catalog.

_________________________________
William E. Williams
Department of Biology
St. Mary's College of Maryland