Cloacina was the goddess of the Roman sewers. She also was the protector of sexual intercourse in marriage. Some believe she was also the goddess of filth, others the goddess of purity. The confusion is understandable given that sanitary sewers carry filth out of the city so that people don't get their togas dirty. Her name derives from cloaca, the Roman word for sewer.
It is understandable also that the Romans would venerate the sewers with a goddess and a shrine given that before the development of the sewer, the alternative was streets brimming with disease-bearing waste. Sewers were a truly a revolutionary development in public health. The Etruscans built the original Roman sewers. Cloacina was very likely an Etruscan deity, and the Romans, as they often did, simply assimilated her. In fact she is sometimes called Venus Cloacina. Given her additional responsibilities to the marriage bed, this is also understandable.
The shrine of Cloacina was in the Roman Forum in front of the Basilica Amelia near where the Basilica's sewer line met the Cloacina Maxima, Rome's main sewer line flowing under the Forum to the Tiber River. The shrine consisted of a ring of marble in the midst of the pavement with a metal fence around it (think manhole.) The ring was about 2.5 meters in diameter. By entering the shrine, you also entered a main maintenance access point to the sewers. Roman coins minted in the time of Julius Caesar show the shrine also including two female statues, one holding a flower. These statues, one apparently Cloacina, either stood above ground alongside the manhole or within the access point.
Though the statues are gone, the marble ring still is visible in the Forum. There is also a marble plaque, added in modern times, marking the spot. The main sewer line, the Cloaca Maxima, is still in service.
and a tour I took while in Rome