Old Sweepy was an undercover Dai Li agent who kept an eye on the Lower Ring of Ba Sing Se and spread misinformation wherever and whenever Long Feng desired. To maintain his cover, he often misled people into believing he was a normal, lovable, talkative old janitor. He had previously worked in the Upper Ring with the top officers of the cultural authority, but was banished by Long Feng into deep cover as a menial laborer after botching an assignment.
Old Sweepy was visited in his warehouse by Team Avatar, who was accompanied by Jet, during their search for information regarding Appa's whereabouts. After Aang discovered a clump of Appa's white fur in the abandoned building, Old Sweepy informed them that they had shipped Appa off to Whaletail Island the previous day. This was false, however, and merely an attempt to lead the team astray and out of Ba Sing Se. In doing so, Old Sweepy hoped to earn his way back into Long Feng's good graces.
Old Sweepy lied and told Team Avatar that Appa had been taken out of Ba Sing Se. Even though Toph was usually able to tell when someone was lying, she was unable to tell that the old man lied, thus implying that the old man was an exceptionally good liar. This makes him the first to lie in Toph's presence without her knowing it. The second was PrincessAzula during the Day of Black Sun.