Pretty much agree w/OG. There are no FW sand sifters comparable w/those in SW. MTS are very shallow diggers (varies with substrate grain size, but never deep). Heavy planting with rooted plants does take pretty good care of the gravel. Fiddler and red-claw crabs are really brackish, not FW, and poor choices in most tanks IMHO. They only scour the surface, which would be better done by shrimp (Amano, Rainbow, Ghost).
The serpentine-bodied loaches do dig through the substrate, but I not convinced there is any cleaning involved.