The workings of an erection question

[O'RileyColt]

When you have an erection, where are the veins that carry the blood out of the penis located? Are they in the corpus spongiosum? Or Does blood, come into and fill the corpus cavernosum, and then lead through the tip of the glans into the the "spongiosum" and out? Are they the veins you see under the surface of your cock? I cant seem to find the exact explanation of what veins actually carry blood out of your erection and where they are.