A clay trap (I am prettey sure) is a plumbing fitting that is basically a
sediment trap that goes on your drain line for your sink. It has a lid that
can be unlatched so that it can be cleaned out when your sink begins to stop
up or drain slowly.
When my art room was built 4 or 5 years ago, the sediment trap was installed
upside down with the lid sitting on the cabinet floor............no way to
clean out that one!