Romans, as we know, had a bit of an obsession with aqueducts and baths, kind of hygiene freaks, they were. Because of this, plumbing was a profession in its own right, and the ancient plumber was called, duh, plumbarius.
Indoor plumbing was not for everybody, only the richest could afford it, and they were charged for the use of the public water network with a fee based on the size of their pipes.
Public latrines in Ostia. Image source here.
Romans were a social bunch, there was a lot of gossip to be dealt with before the social networks appeared online, so latrines were build so as to allow conversation, in case anybody had a bad case of constipation and needed to spend some time in there. There are reports of various emperors (in particular Claudius) who conducted public business from their royal “thrones”.
Public latrines along Hadrian's Wall. Image source here.
Water flowed under the latrines to pick up the mess. Since toilet paper was not available (what do you expect? paper was not available at all), Romans used a sponge on a stick to wipe. Sponges were not disposable, they just dipped them in water to clean the remains of the previous user. (Funny story here: Seneca tells us about a gladiator who was so afraid of his first fight, that he decided to commit suicide before entering the arena. Since gladiators were supervised at all times, the man found a bit of privacy only when going to the loo, so he pushed the sponge down his throat and suffocated himself with it. Death by toilet paper.)
The waste water from latrines, along with what came out of private homes, was collected into a giant sewerage system called Cloaca Maxima. Originally built by Etruscan engineers, it was constantly improved by the Romans. The main drain channel was so big, that a chariot with four horses could be driven through it, if it ever dried up. At some point, the Romans had to cover up their sewers with vaults made of stone, to contain the foul smell.
Interior of Cloaca Maxima. Image source here.
There was even a goddess to preside over the good functioning of the sewerage system, named Cloacina. How cool is that? Though it's unwise to let something of such importance exclusively at the mercy of the gods, so the Romans had city officials, called aediles, who were in charge, among other things, of supervising and improving the sewerage system. It was actually a pretty important position, and people fought to obtain it.
Since the luxury of a water toilet was not available to everybody, the poor population in Rome used regular pots. But, since those ancients were all about recycling and being eco-friendly, nothing was thrown away. People called fullones (meaning cloth launderers) collected pots full of urine from the streets, and used it to launder the citizens' clothes. Well, soap wasn't a common commodity, so they had to use something.
Now, of course, I can't end this quick tour of the Roman toilets without mentioning the anecdote about Emperor Vespasian, the one who introduced fees for the use of public toilets. No credit cards accepted.