I have a 5 gallon bucket with some southdown that I have in old tank water, if necessary on occation I will syphon some of the top layer of my sandbed and use the precured stuff in the bucket to add a new top layer. This isn't something I do very often though. I just wind up sometimes like you said with some bigger pieces of live rock that has fragmented off the larger pieces, as well as small snail shells and other debris, and I only preform this in the front of the tank to keep it nice looking.
Thomas