Assuming all coolant is drained (radiator and engine block), how does the system prime?

I’ve got a car with a radiator punctured near the bottom. There is no coolant in the radiator or in the expansion tank – that much I can see. I assume coolant is gone from the engine block as well (by flowing through lower house into a leaking radiator).

This is pretty much the same condition when we drain coolant from engine block and from radiator doing the flush.

Now, after I replace the radiator and fill it up, some of the coolant will get into the engine block via the lower hose. I expect the air pocket will form in the engine block because thermostat remains closed (it is high on the engine block side and has no hot coolant touching it). As the result, coolant level on the engine block side will be low. The water pump is located quite a bit high as well.

How does the system start to work and circulate the coolant?