Would like to tag a combined sewer overflow but I don’t know how.
The discharge point is described by enclosure Key:outlet - OpenStreetMap Wiki
There’s no format of showing what the =drain
+ tunnel=culvert
+ layer=
is for yet. Not even for it having sewage. utility=sewerage
doesn’t add very much.
If you somehow know where the overflow is diverted from, it could have a waterway=weir