oops...I was thinking about Tribbles I guess.
For a real answer, "Sand sifting" as you are using it, is sort of a misnomer. I am guessing that you want to clean the sand, or at least keep it clean. Sand sifting creatures do sift through the sand, but they eat the small matter (animals, algae too ( I think)) that live in the sand, thereby reducing its biodiversity.
If you really want to keep the sand looking clean, the best bet is to have high flow over the sand, and then to find where detritus collects and syphon that out on a weekly/monthly basis. Then to really keep the sand looking clean, you need to stir or vacuum the top layer...so see, my first answer wasnt total BS!
-Kyle