Inferior thyroid vein drains into -
Venous drainage of the thyroid:-

Superior thyroid vein - Drains into an Internal jugular vein.
Middle thyroid vein - Drains into the internal jugular vein.
Inferior thyroid vein - Drains into a Left brachiocephalic vein.
Fourth thyroid vein of Kocher - Drains into the internal jugular vein.
Internal jugular vein
Superior vena cava
Brachiocephalic vein
External jugular vein