Yes, if they have an entrance on each end. A tunnel=* tag signals the renderer to render an underground passage with an entrance on each side so viewers know they can get out at the other end. It's dangerous to add tunnel=* tags to objects that don't have that other entrance, as it would mislead viewers into thinking they can get out at the other end when they actually can't. They get deeper and deeper into it and potentially get stuck. Note that this particular sewer gets tighter the deeper you crawl into it. Even if you don't get stuck, you may lose orientation. There's no GPS inside and no mobile phone reception, even if you get close to one of the manholes. The danger is real, and armchair mappers have no idea about it. Do you want to be responsible when a serious incident happens? In the best case, OSM would only be in the news for causing a rescue operation. In the worst case, there would be an indictment for manslaughter, and the culprit wouldn't be me, that's for sure. Even if no incident occurs, the risk creation alone is already a violation of Austrian law. The criminal offence is called Gemeingefährdung (public endangerment), § 177 StGB (or now that you know about it, it would be intentional: § 176 StGB – the minimum jail term is 1 year).