What is a sewer backwater valve and who is required to have them?
Most properties have been built so that an obstruction in the public sewer will not cause a sewage backup into the property.
Some properties, however, require the extra protection of a backwater valve in the owners drain line. These properties have been built so that the drain of the lowest plumbing fixture (bath tub, shower, etc.) is lower than the upper manhole of the public sewer. The backwater valve is designed to automatically shut to prevent leakage out of the plumbing fixture if sewage from an obstructed public sewer backs up the owners drain line.
If you have a backwater valve, regular maintenance is required to ensure that it is operating properly at all times.