Sewer lockout device. Back in the old days most of the utilities were privately owned. This device allowed the company to shut off your sewer line if you did not pay your bills. Imagine if these devices were still in use today!
Yes someone thought it was a great idea to take tar paper and roll it into a circle for use as sewer lines. We see these mostly installed here in the US around WWII from 1940-1950. If you have this type of sewer line most likely you have already replaced it. If not, you should or it will become an emergency replacement.