Hello, Andy from the DWG here.
A mapper in Vienna is adamant that an underground drain in Vienna should not have a “tunnel” tag on it. Other people think that it should. A very long changeset discussion is here.
A picture of the exit into the stream to the north is:
I’ve created a thread over in “tagging help and support” to discuss. In order to keep the discussion together, it would make sense to contribute there.