This is the tube that connects the male epididymis to the ejaculatory ducts. It is a continuation of the epididymis.
It starts way down in the scrotum where the epididymis ends and runs up along the spermatic cord, going through the deep inguinal ring where it meets the seminal vesicles. The union of the ducts of the seminal vesicles and the vas deferens is the ejaculatory duct.
The ejaculatory ducts (on both sides) empty into the prostatic utricle (intimately near the prostate gland, silly)