Hey! It seems to me that the tag building=storage_tank describes the facility well. 
You can see from the picture (https://www.google.com/maps/@52.5144235,16.2571003,3a,50y,355.53h,96.48t/data=!3m6!1e1!3m4!1sPIsUgJXi1xaL5rwv3mMeQQ!2e0!7i13312!8i6656) that it is a building - it has solid foundations, walls and a specific roof. If there is a conflict with man_made then the man_made tag should be removed, not building.
I would add roof shape roof:shape=cone to the existing building.

The definition on the wiki https://wiki.openstreetmap.org/wiki/Tag:building%3Dstorage_tank indicates that you should be careful in removing tags, because not every tank is a building. In this case it is a building and a silo at the same time.
Regards.

