Confront the Agent and his Broker with documentary evidence of your discovery, and they may volunteer to pay for the changeover, rather than having you go to Court or having the mistake reported to their E&O Insurance Carrier.
It does sound like simple sloppiness on the part of the Listing Agent . . . . but are you sure that there is a municipal sewer line in your street ?
For Listing Agents, it's often safer to say "unknown" than to lead people to rely on the wrong thing. The three (3) most important words in Real Estate remain "I don't know"; and their use eliminates many lawsuits . . . . yet many Agents refuse to use them !
Some people actually prefer the independence of an on-site waste water disposal system (and my own potable water well) . . . . I'm one of them.
Dale C. Hittle of GOLDEN RULE PROPERTIES in Glover, Vermont
Where We're Always Striving To Put Together "THE FAIR DEAL"