Easement means the legal right to use of private property by others. There are utility easement, meaning utility company use your property to run lines/cables; drainage easement, meaning your neighborhood use your yard to drain rain water. The most common easement is the sidewalk, that the sidewalk is built on your property for other people to walk on. These easement are recorded on your deed, except the utility easement is universal so there is no specific mentions.
A sewer line usually runs undrneath public roads in front of your house. In places where the sewage pipe needs to go under private properties, the water company would need a sewage easement, that is, use a part of the private property to run sewer line. Of course the water company would usually avoid it if they can.
So unless you know there are public sewage lines on private land, you usually can't see the sewage easement.
