|Location||New New York sewers|
|Status||Still spewing sewage|
|First appearance||"The Mutants Are Revolting" (6ACV12)|
Old Filthful is a geyser of sewage in the sewers. It bursts sewage periodically over an exact amount of time. The sewage it spews is most likely the same sewage that is in Lake Mutagenic. It is apparently a popular tourist attraction for mutants. However, Leela found it disgusting after her parents showed it to her.
- Its name is a spoof of the tourist attraction Old Faithful.