Backwater Valves Explained for Homeowners

Why it matters

During an intense downpour the municipal sewer can fill beyond its capacity. Without a valve, the lowest opening in your house, usually the basement floor drain, becomes an overflow for the street. With a valve, that water stops at the flap.

The routine, in order

1. Find the cover. A round or square access lid at floor level, usually close to the front wall where the sewer leaves.
2. Open it twice a year. Lift the lid and look with a flashlight. The flap should hang open, free of debris, paper or grease.
3. Clean gently. With gloves, clear anything caught at the hinge or seat. Some models let the flap lift out for rinsing.
4. Check the cap gasket before you close the lid, so sewer gas stays out.
5. Keep it reachable. Never tile or carpet over the access.

Mistakes to avoid

• Running the washer or dishwasher during a storm backup while the valve is closed. House water has nowhere to go and can rise inside.
• Letting the sump pump discharge into a floor drain upstream of the valve.
• Buying a valve meant for a single fixture and expecting it to protect the whole house.
• Assuming a valve fixes groundwater seepage; it only deals with sewage.

Where a plumber takes over

Installation means cutting the basement floor, working on the main drain and arranging a permit. See our backwater valve page. A valve that will not close, or that keeps clogging, also needs a look.