Emergency Sewer Backup — What to Do Before the Plumber Arrives

Published June 15, 2026 • BBC Rooter & Plumbing • San Fernando Valley

Raw sewage is coming up through the floor drain, the shower, or the toilet. The smell is overwhelming. Your first instinct is to flush again or run the sink — don't. Every drop of water you add makes the backup worse.

You've already called a plumber. The truck is 30 minutes to 2 hours away. What you do right now — in the next 15 minutes — determines whether this is a $500 drain clearing or a $10,000 water damage restoration. Here are the steps, in order.

Step 1: Stop All Water Flow Immediately

Before anything else, stop adding water to the sewer system. That means every person in the house stops using water — no flushing, no sinks, no dishwasher, no washing machine, no showers.

If the backup is actively rising, shut off the main water supply valve. It's typically a gate valve or ball valve near the front of the house where the water line enters, or near the water meter box at the street. Turn it clockwise (gate valve) or perpendicular to the pipe (ball valve) to close it. This kills all water pressure to the house and stops the inflow that's feeding the backup.

If you have a sump pump or ejector pump in the basement, check whether it's running. A failed ejector pump is a common cause of basement sewer backups — and if the pump died, the backup will continue until the pump is replaced or the main line is cleared.

Step 2: Open the Sewer Cleanout (If You Can Find It)

Your home has a sewer cleanout — a capped pipe, usually 3-4 inches in diameter, that provides direct access to the sewer lateral. Common locations: the front or side yard near the foundation, in the garage, or inside a utility closet.

If the cleanout cap is accessible and you can safely reach it, slowly unscrew it. This relieves pressure in the line and may allow backed-up water to drain out through the cleanout instead of into your house. Stand to the side when you open it — if the line is under pressure, sewage will push out.

Important: if the cleanout is already submerged in sewage or the cap won't budge, don't force it. Wait for the plumber. A stripped cleanout cap creates a bigger problem.

Step 3: Protect Yourself — This Is a Health Hazard

Sewer backup water is classified as Category 3 black water by the IICRC — the most contaminated category. It contains bacteria (E. coli, salmonella), viruses (hepatitis A, norovirus), and parasites. Direct contact causes gastrointestinal illness and skin infections.

Before you touch anything in the affected area:

• Wear rubber boots and waterproof gloves (dishwashing gloves work in a pinch)
• Open windows for ventilation — sewer gas contains hydrogen sulfide and methane
• Keep children and pets out of the area entirely
• Do not eat, drink, or touch your face until you've washed thoroughly
• If you have a respirator or N95 mask, wear it — the airborne bacteria in sewer mist are real

If anyone in the household has a compromised immune system, is elderly, or is an infant, they should leave the house until the backup is cleared and the area is sanitized.

Step 4: Turn Off Electrical in the Affected Area

If sewage has reached any area with electrical outlets, appliances, or wiring, turn off the circuit breaker for that area before walking through it. Water and electricity is a lethal combination, and sewer water is more conductive than clean water because of its dissolved solids.

Do not unplug appliances that are sitting in standing water. Shut off the breaker first, then remove them. If your breaker panel is in the affected area (common in garages), call your electrician before touching it — or wait for the plumber and let them assess.

Step 5: Document Everything for Insurance

Standard homeowner's insurance does not cover sewer backup damage. You need a specific "sewer and drain backup" rider on your policy. If you have one, your claim starts now.

Before you clean up a single thing:

• Take photos and video of every affected area — walls, floors, belongings, the water level
• Note the time the backup started and when you discovered it
• Photograph the cleanout and any visible sewage outside
• Save receipts for everything: the plumber, cleaning supplies, damaged items, hotel if you need to leave

If you don't have the sewer backup rider, add it after this emergency is resolved. It typically costs $40-$80 per year and covers $5,000-$25,000 in damage. In the San Fernando Valley, where sewer lines are 50-80 years old, this rider pays for itself the first time you need it.

Step 6: Contain the Spread

While you wait for the plumber, limit how far the sewage reaches:

Block doorways with rolled towels or sandbags to keep water from spreading to unaffected rooms. Use old towels you're willing to throw away — anything that touches sewer water should be discarded, not laundered.

Move valuables up. If sewage is on the floor of a room with furniture, electronics, or important documents, move what you can to higher ground. Anything porous (carpet, upholstered furniture, cardboard boxes) that sits in sewer water for more than 24 hours is typically unsalvageable.

Do not use a shop vac or regular vacuum to suck up sewer water. The contamination will permanently ruin the machine, and spraying atomized sewer water into the air creates an inhalation hazard. Professional restoration companies use specialized extraction equipment rated for black water.

Step 7: Call the Right Plumber

Not every plumber handles sewer emergencies. You need a company with a drain cleaning machine or a hydrojetting rig — not a fixture plumber who primarily does faucets and water heaters. Ask these questions when you call:

• "Do you have a main-line machine?" A main-line drain machine reaches the city connection, not just the branch drains. A cable that only reaches 50 feet won't clear a blockage at 80 feet.
• "Can you run a camera after clearing?" The backup will happen again if you don't find the root cause. A sewer camera inspection after clearing shows exactly what caused the blockage — roots, grease, a collapsed section, or a belly.
• "Are you licensed?" In California, sewer work requires a C-36 (plumbing) or C-42 (sanitation) license. Ask for the CSLB number and verify at cslb.ca.gov.

What Causes Sewer Backups in the San Fernando Valley

Once the emergency is handled and the line is flowing again, the plumber should run a camera to identify the underlying cause. In the Valley, three problems account for 90% of sewer backups:

Tree root intrusion. Ficus, magnolia, camphor, and pepper tree roots enter aging clay and cast iron pipes at the joints. Roots grow into a dense mass that blocks flow. Hydrojetting clears roots immediately, but they'll return in 12-24 months unless the pipe is repaired or relined.

Grease buildup. Cooking grease poured down the kitchen drain doesn't wash away — it solidifies inside the sewer lateral and narrows the pipe over years. Combined with tree roots, a grease-coated pipe backs up during heavy use (holiday cooking, multiple showers). Hydrojetting strips grease to bare pipe, but the habit has to change too.

Bellied or collapsed pipe. A bellied sewer line collects waste in the low point until it blocks completely. A collapsed pipe is a total obstruction. Both require physical repair — either a spot repair or full trenchless replacement — because no amount of snaking fixes a structural problem.

For more on what causes backups specific to Reseda and Van Nuys, see our guide to sewer backup causes in the SFV.

Related reading: Sewer Backup Causes — Reseda & Van Nuys • Sewer Line Cleanouts in the SFV • Sewer & Plumbing FAQ