A storm sewer is for rain water. Like along the side of the road. A sanitary sewer is for toilets. "Never the twain shall meet." (At least most of the time).
If someone is dumping their black tank into the storm sewer, that's a BAD thing.
And a manhole in the street could be either sanitary or storm. I know that some manhole covers say "sanitary" on them, but I would not assume that if it doesn't say sanitary that it must be storm.
I know when I had my septic tank pumped for the 2nd time 30 years ago, the price had jumped from $75 the first time $300 the 2nd time (2 yrs apart). The guy told me that they used to just find a sanitary manhole, pry it up and dump their load in. That's until the city found out what they were doing. Now they have to take it directly to the water treatment plant and PAY to off load it; hence the price increase. (Which probably means some of them are still dumping down a manhole illegally in the middle of the night!!)
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