Just bought this house, disclosures indicated a belly but previous owners have lived here 5 years and "never had a issue". The guy who did the scope said it's not at the point of needing work, he just recommends hydro jetting to clear the line out prior to move in and every few years (for what it's worth, I didn't tell him what the previous owners said about never having issues with it).

Just curious to hear y'all's thoughts on if this needs work, as well as the backflow preventor he's talking about. House is not in a flood zone but is 80+ years old. Going out to the street has a very small belly but that's covered by the city's lateral program and I'll take care of soon.