By the time these cities were built in the 8th to 4th centuries B.C., they had become skilled in making pottery, and mundane items like drain pipes were readily available. Now, on archeological sites they're left in place where possible, but like other old artifacts, if their original location isn't apparent, they're collected and put on one side. Hence this pile of pipes, which don't look very different from the clay pipes we can buy now.
Photo album created with Web Album Generator