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How Mainline Backwater Valves Work

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Marcin from ExpressRooter, the official contractor for Mike Holmes, is here to address some of the common questions that many homeowners ask.

How Mainline Backwater Valves Work

A question that home owners often ask is, how does the mainline backwater valve work in protecting my home? The mainline backwater valve is an essential part of the plumbing system that protects your basement and your assets from a water backup. The way backwater valves operate is very simple; any water that is discharged from the house passes through the valve and the water drains out the other side to the street. In cases where there is a sewer backup, the water will start to back up into the valve and the gate that normally lies flat will close and will remain closed as long as the pressure from the water backup is applied. Once the water dissipates and the pressure is reduced, that gate will open and the flow will be restored. Having a clear cover on the valve will allow a home owner to perform a visual inspection to make sure the valve is operating and that there is no sewer backup.

The mainline backwater valve is what I would call an insurance policy; you’re protecting your house and assets from flooding and damage. You never want to actually see this valve engaged because if it does, that means the city is having drainage problems and your neighbourhood is at risk of flooding. The city and insurance companies do recognize these issues and offer rebates and city subsidies for the valves to help homeowners protect their home from sewer backups.

If you have any questions about installing one of these devices in your home, please call our office at 416-233-2660 or visit our website at

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