As recommended by Tex Gal, do not overfeed. When you do NOT overfeed, the gravel surface remains very very clean. But when there was a need to clean, I found Penn-Plax's Air-Vac to be quite effective:
http://www.shopwiki.com/detail?s=343833&o=151069425
Oh, I almost forgot my clean-up crew - the pond snails. They do a very good job at picking up any left over. Thus, the gravel surface remains spotless.
