You have to be careful throwing little critters down there as they might get sucked into your return pumps, skimmers, etc. I think some people just take an old maxijet or something similar to suck out their sump. Stir it up real good and pump out the crude.
If your pump is in a different section as where you want the CUC, I think it would be fine. It really depends on what you are trying to clean up...for detritus, if you have sand, some nass snails, and some hermtis should do the trick.