In the city, you generally don't have to worry about what happens after you flush. It's gone off your property, and unless it pollutes the beach, it's not your problem.
Like any other system, a septic system can be fine or it can be trouble. Trouble is expensive. A new septic system requires an approved cement or plastic tank, and a large tile or weeping bed. It will cost from $4,000 up. That is an estimate. Always check with a couple of service providers.
The Environmental Protection Act provides, "No person shall use or operate a sewage system or any part thereof that has been constructed, installed, established, enlarged, extended or altered after the 15th day of April, 1974, unless a permit for its use or operation has been issued."
So, the first question becomes, when was the system installed? If it was before April 15, 1974, no permit was needed and you must remember that that means no official inspection was done. Getting some kind of inspection and a vendor's warrant that the system has been working properly, should be a priority.
Even for systems installed since 1974, you have to consider the fact that it could be up to 25 years old. Ask about its history, and how has it been working? Will the vendor state in writing that he has had no problems?