The house might well be connected. The are looks rural and empty on one side, but on the other side is the village.
But why did the Police drain the overflow if the system is no longer in use??
The problem might be with the slope of the property. If the house was built around 1900 with a septic tank or well, then all drains would flow in the direction of the well in the back of the garden. This puts the house on the highest point so to speak, at least for the drains.
So if a modern sewage system is built from the main road in front of the house, you have a problem, because all your pipes are going the other way, and water does not flow uphill by itself. Plus you have to connect the system from the lowest point and that would be the garage. According to the info, the garage has a guestroom with facilities.
We had the same problem. The council wanted to connect our house to the sewerage at the side of the front door, but that was not possible with all the pipes leading to the back of the garden. They had to dig a long trench in the backyard AND install a pump on public ground (because the pump was theirs). It was all very complicated and expensive. Fotunately the fee for the home owners is the same in all cases.