http://www.npr.org/templates/story/s...toryId=5238296 doesn't answer about the actual chemical being dangerous, but the sewer gases coming up the pipes is what will hurt ya'. Gross.... anyone that has been near any raw sewage knows that smell will burn nose hairs an eyeballs right out of their sockets.
Ok maybe not that bad, but it's pretty disgusting. Unless you like that smell. Then you're just plain crazy.