SU 5876 is made up of smaller drain cover slabs underneath the floors of room 22. It appears to form a Y junction with the drain covered by slabs SU 5871, presumably draining thence to the south beneath in situ features. In fact, there is evidence of mortar patching on the southern side of the room, as well as beyond threshold 5823 further south. There is evidence of mortar patching throughout, signifying that there could have been later repairs done.