You can use another container, such as a bowl or pitcher. It just needs to be big enough to hold a little over 4 cups (950 mL) of liquid. This will give you enough room for the other ingredients.  You can use less water if you want to. You'll need to adjust the amount of the other ingredients, however. The exact temperature of the water does not matter. You can use the warmest water from your tap, although distilled water would be better.

How would you rephrase that briefly using Vietnamese?
Rót 4 cốc (1 lít) nước ấm vào một chiếc lọ to.