The main vein that drains the coronary circulation is the

Coronary sinus

Explanation:

The coronary sinus is usually referred to as the principal vein that is connected to the heart. It is found to be present on the posterior region within the coronary sulcus. This coronary sulcus is connected between the left atrium and the left ventricle. This sinus is present in all the mammals and human beings.

This coronary sinus is also considered as the main collector of blood and allows the less oxygenated blood to flow into the right atrium.