You’re right, I had to look it up.
Gongfermors or gong-scourers were men who went round emptying medieval previes and cesspits.
Where there was no convenient moat or stream, people dug a pit, or used a removable barrel. In either case the sewage had to be removed in due course. In 1281, 13 men took five nights to clear the cloaca at Newgate Prison-—on triple pay! At Hampton Court in Henry VIII’s time the gongfermors had a formidable task.