Re: how does......
Good Morning liftloop,
I've not heard of a "Trap Sluice" though there is the "Le Trap Sluice" and the AU gold trap sluice by Angus McKirk. Both of these are "drop riffle design" sluices. Basically the riffle drops into the bottom of the sluice, the riffles do not stand above the bottom of the as do the Keene sluice boxes. OK, so that picture may look a little muddy so let me try another explanation. Let us assume there is a 4 foot long by 8 inch wide pine board and we take a circular saw and cut grooves across the board the 8 inch width of the board. Lets say we leave a half inch space between each groove. These grooves are "Drop Riffles", the heavy materials "drop" into the riffles or grooves. The grooves can be different widths, 1/8", 1/4", 1/2" as examples and "Astrobouncer", a Tnet member, has posted many a picture and video about the drop riffle sluices he builds and uses, check them out. Also just Google "trap sluice" and see what comes up.
But there may be a sluice that is called a "Trap Sluice" so lets see who else posts on this thread.
Good Luck as it sounds like you are getting interested, 63bkpkr