SU 5401 runs east to west, south of the ashlar wall 5006/7. It is covered by both SU 5314 and the opus incertum wall SU 5402. The wall 5402 covers the drain 5401, which continues under the wall and is covered by SU 5379 on the western side of the wall 5402. The drain is also likely to continue under the opus reticulatum wall SU 5302. The drain is made up of eight blocks. The wall 5402 defines the western excavation limit. The stairs SU 5405 abut the drain SU 5401 on the eastern excavation limit. The drain 5401 sits into a cut into the bedrock ( cut SU number not given yet). Given the poor state of preservation of this part of the complex, it is unclear whether the drain was covered by or formed part of the original floor, though the latter seems more likely. The concavity and consistent gentle slope from east to west of this feature make its function as a drain almost certain.