Cut in tufo bedrock for the construction of drainage channel along north and west walls of room 21. The tile lining SU 5832 and opus signinum 5828-31 were applied within the cut to seal the channel. The N-S channel slopes down to the north, presumably drawing water from a sewer under the street or from the baths across the street. At the northwest corner, an additional channel flows under the street and enters the E-W channel at a sharp angle. The bottom of the north cut then slopes down to the east, presumably connecting with the north-south cut SU 5802 along the eastern wall of the room, where it drains to the south. This relationship was not uncovered due to the desire not to undercut a feature in the northeast corner of room 21. All together the features suggest that the room served as a latrine.