Sewer rats carry real health risks, but they rarely attack people directly
Sewer rats are dangerous primarily because of the diseases they carry and the damage they cause to pipes and foundations—not because they bite. The most common sewer rat is the Norway rat, which lives in underground spaces and travels through pipes looking for food and nesting material. These rats shed urine and feces as they move, contaminating surfaces they touch. They can spread leptospirosis (a bacterial infection from rat urine), hantavirus, and salmonella. A rat in your sewer system is a sign that entry points exist between the sewer and your home.
Rats avoid humans when possible. A sewer rat will flee rather than confront you. The danger comes from what they leave behind—contaminated water, gnawed pipes that leak, and entry holes they create or enlarge. If you see a rat in your home or smell a strong musky odor near drains, the sewer connection is compromised and rats may already be inside your walls or basement.
Key Takeaways
- Sewer rats spread diseases through their urine and feces, particularly leptospirosis, which enters your body through cuts or mucous membranes.
- Rats gnaw through clay pipes, PVC, and concrete, creating cracks that allow sewage to leak into your foundation and soil.
- A rat in your sewer indicates a gap or hole large enough for rats to enter—usually a broken pipe section or a gap where the sewer line meets your home's foundation.
- Trapping a rat in your home does not solve the sewer problem; you must locate and seal the entry point or the rats will return.
- Professional sewer camera inspection can show exactly where rats are entering and whether your pipes are damaged.
How sewer rats enter homes through pipes and cracks
Sewer rats do not swim up through toilet bowls in the way urban legends suggest. Instead, they enter through breaks in the sewer line itself. A rat can squeeze through a hole the size of a dime. As the rat moves through the pipe, it gnaws at the edges, making the hole larger. Over weeks or months, a small crack becomes a gap wide enough for a rat to pass through repeatedly.
The most common entry points are where the sewer line connects to your home's foundation, where old clay pipes have cracked, and at the base of the toilet flange (the ring that seals the toilet to the floor). Rats also enter through gaps around pipes that pass through exterior walls. Once inside, they follow the pipes into walls and crawl spaces, where they nest in insulation and behind cabinets.
If you have an older home with clay sewer pipes, the risk is higher. Clay pipes crack from ground settling, tree root intrusion, and age. PVC pipes are more resistant to gnawing but can still be damaged if rats have been in the line for months.
Diseases sewer rats transmit and how exposure happens
Leptospirosis is the most common disease from sewer rats. The bacteria lives in rat urine. You can catch it by touching contaminated surfaces and then touching your mouth, nose, or eyes, or by getting rat urine in a cut on your skin. Symptoms appear three to fourteen days after exposure and include fever, headache, muscle aches, and sometimes kidney damage. It is treatable with antibiotics if caught early.
Hantavirus is rarer but more serious. It spreads through dried rat droppings that become airborne when you sweep or vacuum. Breathing in the dust can cause a respiratory infection. Hantavirus has a high death rate in people who develop symptoms, though infection is uncommon.
Salmonella spreads the same way as leptospirosis—through contact with rat feces or urine. It causes severe diarrhea and fever. Rats also carry rat-bite fever, though this requires an actual bite, which is rare.
The risk is highest in basements, crawl spaces, and areas where rats have nested. Cleaning up rat droppings without proper protection (gloves, N95 mask, and ventilation) increases your exposure. If you find droppings in your home, do not vacuum them; spray with a disinfectant first, let sit for five minutes, then wipe with paper towels.
Structural damage rats cause to sewer lines and foundations
Rats gnaw constantly because their teeth never stop growing. In a sewer line, they chew through clay, PVC, and even concrete over time. A single rat can create multiple holes; a family of rats can destroy a section of pipe in months. Once the pipe is breached, sewage leaks into the soil around your foundation.
This causes several problems. Sewage seeping into the ground weakens the soil, leading to foundation settling and cracks in basement walls. The wet soil also attracts more rats and creates conditions for mold growth. If the leak is large enough, you may see sewage backing up into your basement or notice soggy patches in your yard.
Repair costs vary widely. A small crack sealed with epoxy costs $300 to $800. Replacing a section of sewer line runs $3,000 to $25,000 depending on depth, length, and whether the line is under a driveway or foundation. Catching the problem early—before major structural damage occurs—saves thousands in repairs.
Signs that sewer rats are present in your system
The first sign is often a rat sighting in your basement, crawl space, or kitchen. You may also notice a strong musky smell near drains or in the basement—this is rat urine. Droppings are another clear indicator. Rat droppings are dark, about the size of a grain of rice, and often found in clusters near walls or in corners.
Listen for scratching sounds in walls or under floors, especially at night when rats are most active. You may hear squeaking or the sound of something moving through pipes. Gnaw marks on wood, plastic, or insulation are also a sign. Rats often gnaw on the corners of boxes and the edges of wooden beams.
If your toilet gurgles, drains back up, or you smell sewer gas in your home, the sewer line may be cracked. This does not always mean rats are present, but it means the line is compromised and rats could enter. A professional plumber can use a sewer camera to see inside the line and confirm whether rats have created holes.
What to do if you suspect sewer rats in your home
Start by calling a licensed plumber or pest control company that specializes in sewer work. Do not attempt to trap rats in your home without addressing the sewer entry point—you will catch a few, but more will enter. A professional can perform a sewer camera inspection, which costs $300 to $600 and shows exactly where rats are entering and whether pipes are damaged.
If rats are confirmed, the plumber will recommend either sealing the entry point (if the damage is minor) or replacing the damaged section of pipe. Sealing alone works only if the hole is small and there is no ongoing damage. If the pipe is actively cracked or if rats have enlarged the hole significantly, replacement is necessary.
While waiting for the plumber, seal obvious entry points in your home. Caulk gaps around pipes where they enter walls. Use steel wool and caulk around the base of the toilet. Remove food sources—store dry goods in sealed containers, do not leave pet food out overnight, and keep trash in sealed bins. These steps reduce the rat population inside your home but do not stop new rats from entering through the sewer line.
Preventing sewer rats from entering in the first place
Prevention is easier than removal. Have your sewer line inspected every five to ten years, especially if your home is older than thirty years or if you have had previous rat problems. An inspection costs $300 to $600 and can catch small cracks before rats find them.
Keep tree roots away from your sewer line. Roots crack pipes as they grow, creating entry points. If you have large trees near your sewer line, ask a plumber whether root barriers or periodic root removal is needed. Do not plant trees directly over the sewer line.
Maintain your gutters and downspouts so water does not pool near your foundation. Rats are attracted to moisture. Fix leaking pipes inside your home promptly. Keep your basement or crawl space dry and well-ventilated. Store firewood, cardboard, and other nesting materials away from the foundation.
If you live in an area with known sewer rat problems, consider installing a one-way door (called a rodent exclusion valve) on your sewer vent stack. This allows gases and water to exit but prevents rats from entering. Installation costs $200 to $400 and is most effective when combined with sewer line repair.
Frequently Asked Questions
Can a sewer rat come up through my toilet?
Rats can enter through the toilet if the sewer line is cracked near the toilet flange or if the wax ring seal is broken. However, they typically enter through cracks in the sewer line itself, not by swimming up from the main sewer. If you see a rat in your toilet, the sewer line is definitely compromised and needs inspection.
What should I do if I find rat droppings in my home?
Do not vacuum or sweep them dry. Spray the area with a disinfectant (bleach solution or commercial disinfectant) and let sit for five minutes. Wipe up with paper towels and dispose in a sealed bag. Wear gloves and an N95 mask. Ventilate the area well. If droppings are extensive, contact a professional cleaning service that handles biohazard cleanup.
How much does it cost to fix a sewer line damaged by rats?
A sewer camera inspection costs $300 to $600. Sealing a small hole costs $300 to $800. Replacing a damaged section of pipe ranges from $3,000 to $25,000 depending on the length, depth, and location of the line. Get quotes from at least two plumbers before deciding.
Will poison kill sewer rats?
Poison can kill rats in your home, but it does not solve the sewer entry problem. Rats will continue to enter through the damaged line. Poison also risks poisoning pets and wildlife. Trapping combined with sewer line repair is more effective and safer.
How long does it take to get rid of sewer rats?
Trapping rats in your home takes one to three weeks if the sewer entry is sealed. If the entry point remains open, new rats will keep arriving. Sewer line repair takes one to three days for a small section, longer if the line is deep or under a driveway. Plan for the full process to take four to eight weeks from inspection to final repair.