I tend to argee with Gaius in that I think we tend to overly generalize the sanataion conditions across the board in various locals throughout the span of the ancient world.
The evidence seems to indicate that in Rome proper for most of it's history, sanitation was of course a high priority. Not remembering the exact reference but Strabo discusses it in length when talking about Rome.
Rome undoubtably had street cleaners to suppliment it's celebrated sewer system. I don't know the Latin word is but a verb in Greek for cleaning away refuse is anakatharsis. It had to be quite similar to what Appian describes in his treatment of the 3rd Punic War (because Carthage's housing blocks were laid out with spillways for refuse to be cleaned out by a public service):
"The street cleaners, who were removing the rubbish with axes, mattocks, and forks, and making the roads passable..."
But, back to Gaius' original question:
If you dig into it, you find it quite evident that the Romans used that kind of refuse extrensively to level ground during building/engineering projects. Many archaeology sites have been preserved because the Romans covered old thing over with such rubble!