The Nassarius Snail is a great scavenger that will eat various kind of organic material such as fish waste, leftover foods and even dying or death fish, making it a beneficial addition to your tank. Another benefit of having these snails in your tank is that they will also help to aerate the sandy substrate of your tank as they sift through the substrate while searching for food. This action also helps to reduce the growth of slime algae or cyanobacteria on the substrate surface. They also have the habit of burying their whole shell in the substrate, with only siphon protruding above the substrate. This siphon is used to sense the presence of food. They will move quickly, often as a group towards the food source once food is detected.
It would appear we are both right. I think that they are some of the neatest inhabitants in a saltwater tank and are really the one thing that got me into the saltwater side of things after watching them popp out of the sand in my brothers tank.
To the op I hope the info helps you with your dirty sand and of course more flow will help as well.