A check valve is a sure way to avoid sewer backups. That is why municipal by-laws require all property owners to install check valves in their homes regardless of the age of the building.
The municipal by-law provides that check valves must never be fitted to a home's primary sewer pipe system, but rather to the secondary sewer connection pipes. The foundation drain also have to be protected by a check valve.
As well, check valves must be maintained in good working order and regularly checked.
Check valves must remain accessible at all times to allow for regular maintenance at least twice a year, normally in the spring and in the fall, when the clocks are reset.
If a check valve is located in a wall or under the basement floor, there should be an access panel.
The following should be checked:
IMPORTANT: Never open the check valve during a sewer backup.
(Source: Ville de Sherbrooke)