Mine never liked pvc tube, they just crawled out somehow and sat next to it. I've got two side by side, they don't mind each other's touch.
My bangais seem to take advantage of their position in the current, and stay very very close to them, without ever being harmed. The coral banded shrimp occasionally gets a whipping, but takes revenge by nipping off a few tentacles and eating them.
I saw one of them eat sand once... maybe it needed to build/repair its tube, or maybe it 'smelled' something decaying in that spot. They can eat A LOT. When I first got one I fed it repeatedly to see when it would stop... it never did! I stopped feeding it because I was worrying about water quality.
Fascinating creatures to watch. I've never had any troubles with them. I'm always on the lookout to get another one in a different color.