No siphon here , Vleeschgracht cross the Senne here : https://www.openstreetmap.org/way/446474068

https://geodata.environnement.brussels/client/view/0004a8db-589d-4498-b9b9-87d7b7d7f187

I propose to tag the culvert like this https://www.openstreetmap.org/way/818702147 ; so we keep the way when we can have data from vivaqua  but definitivly there's no Petite Senne - Klein Zenneke that pass there.