What does "sink and copper" mean in British parlance circa 1937?

Comments being ephemeral, I am posting the (partial-answer) comment above, by @BillJ, pending a more complete one either by himself or someone else:

A "copper" was typically a large metal tank of upright cylindrical shape, used for heating sufficient hot water for a bath or some task that required a large quantity of water. Once heated, the water was drained into the bathtub, sink or whatever. They were very common in British homes up until the advent of central-heating systems or 'back-boilers' and other systems.

I recall that my parents had a gas-powered boiler that was kept in the scullery. It was pulled out on bath-days and connected to an adjacent gas tap on the wall in the bathroom!

So, a copper seems to be (a small equivalent of) what in Canada today is referred to as "the hot water tank"; and which is usually situated in the basement of Canadian houses but might be located on the main floor of a ranch-style house or condominium. However, from the personal comment quoted above by @BillJ it seems that this object might occasionally be a chattel rather than a fixture. In contrast, a sink would always be a fixture, the chattel equivalent being a wash basin or wash stand.

As I read further through The Road to Wigan Pier it becomes evident that Orwell is consistently very precise and exact in his phrasing and use of words. This gives credence, in my eyes, for the validity of drawing the distinction above.

Here is the laundry copper referred to below @BoldBen, with his comment text

The point is that the "wash copper" was heated by its own solid fuel fire with its own chimney and was not a hot water tank like the one you describe. As Orwell mentions other houses having a scullery I believe that he meant the dedicated wash copper.