Why Does My Drain Smell Like Sewage After Heavy Rain?

When heavy rain saturates the ground, stormwater can enter the sewer system through cracks or illegal connections. This extra volume raises the water level and can push sewage gas back through the lowest drain in your home. The gas smells like rotten eggs or sewage, and it often appears right after a storm passes.

A clogged or improperly installed vent pipe on your plumbing can also cause the problem. The vent pipe lets sewer gas escape safely through your roof. If it's blocked by debris or a bird's nest, the gas has nowhere to go except back into your house. A dried-out drain trap, common in rarely used sinks, can also let odors rise.

Start by running water down every drain in your home for a minute or two. This refills the water traps that block sewer gas. If the smell is strong, open windows and use fans to move air out. Keep the area ventilated until the odor fades.

If the smell persists after running water, the cause may be a damaged pipe or a sewer backup. In that case, you might have sewage inside your walls or under the floor. Turn off the water to that drain if you can, and avoid using it until the problem is checked.

You can reduce the chance of this happening again by keeping your drains clear. Avoid pouring grease or food scraps down the kitchen sink. Use drain strainers to catch hair and debris, and clean them regularly.

During the rainy season, check your yard for low spots where water pools. Make sure your downspouts direct water away from your foundation. If your home has a crawlspace, consider a sewer backflow valve, but you'll need a plumber to install it.