Are we talking storm drains or body waste removal?

In Rome itself, the creation problem was approached backwards. The area around the seven hills was swampy, which was useful as a boundary, but problematic for growing a city. So, according to Livy, the natural channel was regularized, made narrower, walled in with stone, and initially open to the air and sluiced out to the Tiber river. Over time (and core samples have confirmed this) the swampy area was filled in with soil, raising the walking surface considerably. Over more time, they covered the canal completely and called the Cloaca Maxima which opens onto the river to this day (and yes, it was well known in the 19th century). Subsections went out as well, and were connected to the wider city, the public baths, even the Colosseum. The only problem was that when the river flooded, as it did regularlry, the water came back up through the system. Not so nice.

It was not primarily intended as the prime means of removing raw human waste. Night soil was collected and used for fertilizer, urine famously collected and used to bleach cloth (the emperor Vespasian taxed urine, and when his sone said that was undignified, observed that the money it brought in didn't smell). Which is not to say that human and animal waste did not wind up there, they did, but that was not the primary function.

So, to your question - knowledge of Roman sewers was widespread for centuries, but the will power and man power to make them happen didn't seem worth the candle. Why change a system (slop buckeets) that had worked for centuries? What changed was the cholera outbreak in London in 1858 when the summer heat and the sluggish water created the Great Stink. Only then did they make the connection between waste water and disease. Between the smell and illness, the powers that were finally did what the Roman's had done centuries earlier - but again, the Romans were not doing it for their health.

I have a general audience book coming out in November which deals with many matters concerning the Tiber, and the Cloaca Maxima makes up a chapter in it.