Hi,

tunnel=yes isn't always appropriate to tag a drain/stream/river going underground. Just because tunnel=yes may be understood to be an actual drain inside a tunnel where humans can go.

I use to tag underground drains as waterway=drain + (man_made=pipeline) + location=underground without any tunnel tag.
https://www.openstreetmap.org/way/243333009

It makes them appear on OSM Carto like overground ones.
I find location=undergound enough to show them with dashes

Thank you in advance to consider this potential issue