Help me out here.

[tim the toolman]

This also concerns me.

violet. The animal forms a small, calcareous shell mound and then sends up a short, three to five millimeter long, vertical stalk. The upper edge of this tube may be razor sharp, and may inflict rather nasty cuts. A few of these would be no real problem; however, this animal reproduces very well in marine aquaria. Left unchecked, it can reach populations of over several thousand in a few months. They prefer high current areas, and will infest and clog plumbing, significantly reducing water flow. In severe infestations they can clog and shut down pumps. The only solution in cases like these is physical removal of the animals using whatever method is easiest (a muriatic acid bath works well).

From http://reefkeeping.com/issues/2005-01/rs/index.php