Looking After a Backwater Valve

The entry in brief

Open the access cover, look for debris around the flap, clean it gently, and make sure the flap moves and seals. Do it in spring and autumn.

Where it is

It is set into the main drain below the slab, most often a few feet in from the street-side wall. You will see a round or rectangular cover set into the floor. If it is under carpet or a cabinet, you will need a way to reach it.

Checking it, step by step

Avoid running water in the house while the cover is off.
Remove the access cover, wearing gloves.
Look at the flap and the area around it for paper, grease or debris.
Use a hose or bucket of water to rinse it clean if needed.
Check that the flap opens and closes freely.
Replace the cover and check its seal.

N.B. If the flap is stuck, cracked or the valve body looks damaged, call a plumber rather than forcing it.

During a storm

When the city sewer backs up, the flap closes. With the flap down, your own drains have nowhere to go either. Hold off on laundry, dishes, showers and flushing until the storm passes.

A backwater valve works best with a sump pump that discharges outside, extended downspouts and good grading. Our basement flooding note covers the full picture.

What callers want to know

Is there one in my basement already?

Look for an access cover on the basement floor near the main drain. Many older homes do not have one.

Can a valve be added to an existing home?

Yes. See our backwater valve installation page.