First the duster, Just leave the tube alone. There is no need to remove it.
Second, the smaller duster are nice hitchhikers and are not the type that grows large. here is a link that you might enjoy:
Live Rock Hitch Hikers
What type of gobie do you have. Some, maybe most will feed on brisle worms and animals that live in your sand and liverock. They be look thin but that might just be the way they are. Do not overfeed. It could become a bad habbit...
You did not say how long you where going to be away.
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