Final answer:
The oesophageal vein drains its blood into the azygos vein via the superior intercostal vein.
Step-by-step explanation:
The oesophageal vein drains its blood into the azygos vein through the superior intercostal vein. The oesophageal vein collects blood from the esophageal veins of the esophagus and the left intercostal veins. The blood then flows into the superior intercostal vein, which connects to the azygos vein.