As I see it, it is not a tank, but rather a manifold to support the two valves/taps. An example of a "modern" one (similar ones in plumbing are still hand made

As I see it, it is not a tank, but rather a manifold to support the two valves/taps. An example of a "modern" one (similar ones in plumbing are still hand made on the spot with pipes, but this is a pre-fabricated one): https://media-www.canadiantire.ca/product/fixing/plumbing/rough-plumbing/0631319/4-outlete-manifold-copper-25861199-e552-4101-8548-5cc251a1b9e5.png?imwidth=1024 https://media-www.canadiantire.ca/product/fixing/plumbing/ro...