If your drains smell like rotten eggs or sewage, something is wrong. A healthy plumbing system should not produce noticeable smells. Troy Plumbing Co serves homeowners in Troy, NY diagnose and eliminate drain odors. This guide explains what causes smelly drains and what you can do about it.
Dried-Out P-Traps
The most common and easiest-to-fix cause of drain odors is a dried-out P-trap. The P-trap is the U-shaped section of pipe under every sink, shower, and floor drain. It holds a small amount of water that acts as a seal against sewer gases. When a drain goes unused for several weeks or months, the water in the P-trap can evaporate, breaking the seal and allowing sewer gas to rise into your home through the open drain.
This is extremely common in guest bathrooms, basement floor drains, utility sinks, and any fixture that is not used regularly. The fix is simple: run water in the fixture for about a minute to refill the P-trap. For floor drains, pour a gallon of water directly into the drain. If the odor disappears within a few hours, the dried P-trap was the problem. To prevent it from recurring, make a habit of running water in unused drains every few weeks, or pour a small amount of mineral oil into the drain, which floats on top of the water and dramatically slows evaporation.
In very dry climates or homes with aggressive HVAC systems that pull humidity from the air, P-traps can dry out surprisingly quickly. If you have floor drains or fixtures that go unused for long periods, the mineral oil trick is especially useful.
Organic Buildup in the Drain
Over time, a slimy layer of bacteria, mold, and decomposing organic matter builds up on the inside walls of your drain pipes. This biofilm feeds on soap residue, hair, skin cells, food particles, and other organic matter that washes down the drain. As the bacteria decompose this material, they produce foul-smelling gases including hydrogen sulfide, which has the characteristic rotten egg smell.
Bathroom sink drains are particularly prone to biofilm buildup because of the combination of soap, toothpaste, hair, and warm moisture. Kitchen drains accumulate food grease and particles that feed bacterial growth. The buildup is usually concentrated in the first few feet of pipe below the drain opening, including the P-trap and the overflow passage in sinks.
To clean biofilm from a drain, start by removing the drain stopper or screen and cleaning it thoroughly. Pour half a cup of baking soda into the drain, followed by half a cup of white vinegar. Let it fizz for 30 minutes, then flush with very hot (near boiling) water. For persistent odors, use an enzyme-based drain cleaner that digests organic matter without damaging pipes. Avoid chemical drain cleaners, which can damage pipes and do not effectively address biofilm.
For bathroom sinks with an overflow hole (the small opening near the top of the basin), clean it by pouring a small amount of enzyme cleaner or baking soda solution directly into the overflow. Biofilm inside the overflow passage is a frequently overlooked source of drain odors.
Plumbing Vent Problems
Every drain in your home is connected to a vent pipe that extends up through the roof. The vent system serves two purposes: it allows air into the drain system so water flows smoothly (like removing your thumb from a straw), and it directs sewer gases up and out through the roof where they dissipate harmlessly into the atmosphere. If a vent pipe becomes blocked or damaged, sewer gases cannot escape through the roof and instead find their way back into your home through the drains.
Vent pipes can become blocked by bird nests, leaves, ice buildup in winter, dead animals, or debris. A blocked vent also causes drainage problems because without proper air flow, water draining through the pipes creates a vacuum that pulls water out of P-traps (breaking the seal) and causes slow, gurgling drains.
If you hear gurgling sounds when drains empty, smell sewer gas from multiple fixtures, or notice that drains are slow throughout the house, a blocked vent is a likely culprit. Clearing a vent blockage requires accessing the vent opening on the roof, which is a job for a professional due to the height and safety concerns involved.
Sewer Line Problems
Persistent or widespread drain odors that do not respond to simple fixes may indicate a problem with your main sewer line. A cracked, broken, or separated sewer pipe can allow sewer gas to seep into the surrounding soil and enter your home through foundation cracks, failed pipe joints, or compromised seals. Tree root intrusion into sewer pipes creates gaps where gas escapes. A partially blocked sewer line can cause wastewater to back up and produce odors throughout the home.
Signs of a sewer line problem beyond odors include multiple slow drains, gurgling sounds from toilets when other fixtures drain, wet spots or sinkholes in the yard, and unusually lush patches of grass over the sewer line. A sewer camera inspection is the best way to identify sewer line problems. The camera reveals cracks, root intrusion, offsets, bellies, and other issues that may be causing odors and drainage problems.
Garbage Disposal Odors
Garbage disposals are a frequent source of kitchen drain odors. Food particles get trapped on the splash guard, grind chamber walls, and in the crevices of the grinding components. These trapped particles decompose and produce unpleasant smells. The warm, moist environment inside the disposal is ideal for bacterial growth.
To clean a smelly disposal, start by cleaning the rubber splash guard. Lift each flap and scrub the underside with an old toothbrush and dish soap. Then run a handful of ice cubes and a cup of rock salt through the disposal to scrub the grind chamber. Follow with lemon or orange peels for a fresh scent. For a deeper clean, pour half a cup of baking soda into the disposal, let it sit for 30 minutes, then add a cup of vinegar and let it fizz before flushing with hot water while running the disposal.
Run your disposal regularly with cold water, even when you do not have food to process. This prevents standing water and food residue from accumulating and decomposing.
When to Call a Professional
Persistent drain odors can indicate serious plumbing problems that need expert attention. Troy Plumbing Co provides thorough drain diagnosis and repair services in Troy, NY. Our licensed plumbers can identify the source of drain odors, clear blocked vents, inspect sewer lines, and resolve the problem permanently. Call 5183631507 to schedule a drain evaluation.