From the National Trust guidebook:
"The central ground-floor projection was added later and probably contained garderobes or privies.
John Brome would have had two in this wing, one for the bedrooms on the upper floor... and the other
behind the later projection. The effluent from these would have drained into the medieval sewer.
To clean out the sewer from time to time, the water level in the moat would have been raised
and then lowered, using the outlet sluice."

Lovely!