The Romans liked keeping their city neat and therefore had lots of public toilets scattered throughout the city. They also famously had a sewage system, but not surprisingly, not every toilet was connected to it. Not by a long shot. All those public toilets just had large containers under them, which if left alone would eventually fill up. But luckily, ancient Romans were like the MacGyver's of piss.
Emperor Vespasian was the first one to realize he was quite literally sitting on a liquid gold mine. He started sending people out to collect urine, which he got for free, and then sold it to a huge variety of workmen in the city. These workmen paid a tax for the use of the urine, which was easier than going out and rounding it all up themselves.
Obviously. Wait, what?
So just what did they do with it? Let's just say everyone in Rome must have been walking around smelling like a latrine: Tanners used it to soften leather, and it was especially practical in the laundry, where it was used to get togas that famous bright white. So the city stayed clean, everyone had nice clothes and the government took in lots of tax revenue. Everyone wins.
Finally, drunken urination pays off.