Sewer is backed up
Woke up this morning and the sewer seems to be backed up. We have a utility sink in the basement that the washer drains into. It is the lowest drain in the house and had about 3" of water in it. I called the township and am waiting for them to take a look at their side. There is a cast iron piece where the sewer enters/exits my house that has a little water on the top of it. Does anyone know what this piece is and what it does? Attached is a picture. Thanks.