Figure out when the smell shows up
The timing of the smell points to the cause before you touch anything.
- Smells right after the shower runs, especially warm and musty. Biofilm and hair in the strainer and the trap.
- Smells only in a shower or tub nobody uses. A trap that has dried out.
- Smells with a gurgle as the water leaves, or when a toilet flushes. A vent problem.
- Smells like sewage, strongest in the morning or after a stretch of no use, in more than one drain. Sewer gas from the line itself.
- Smells like rotten eggs only when you run hot water. That one often has nothing to do with the drain, and we cover it below.
Why does my shower drain smell like rotten eggs or sewage?
A rotten egg smell from a drain is hydrogen sulfide, the gas that the federal toxic substances agency says is often called sewer gas. It reaches your bathroom when the water seal in the trap is gone (dried out or pulled out by a vent problem) or when there is a leak or blockage in the line itself. Start with the free fix: run the water for a full minute and see whether the smell goes. If it does, the trap was dry. If it comes back within a day or two, read on to the vent and larger-line sections. If only the hot water smells, skip to the water heater section.
Cause one: biofilm, soap and hair
This is the cause behind most smelly shower drains, and it is the answer when a drain smells musty, sour, like mildew or like body odor. Every shower leaves a thin layer of soap, skin oil, shampoo and hair on the strainer, the drain body and the walls of the trap. Bacteria feed on it. Over weeks it builds into a slick film, and when the water warms it up, it gives off a sour, swampy smell that drifts up through the strainer.
Fixing it means removing the film, and covering it up will not do that.
1. Take the strainer cover off (a screwdriver, or pry up a snap-in cover) and pull out every bit of hair you can reach. If the cover will not come off, do not force it. Work a strip through the slots instead.
2. Scrub the cover and the inside of the drain opening with an old toothbrush and dish soap. You are removing a coating, and rubbing does more than soaking.
3. Slide a barbed plastic strip down the drain and pull it back out. It will usually bring up a grey, slimy rope that explains the smell on the spot.
4. Pour a kettle of hot tap water, not boiling, down the drain to rinse.
After that, a monthly dose of an enzyme cleaner (such as Green Gobbler) can slow the film from returning. Enzyme cleaners are a different category from caustic and acid openers: the makers describe them as slow-acting maintenance products, with label directions that call for waiting several hours before running water, and one major brand states its enzyme maintenance product will not open clogs.
Will vinegar help a smelly drain, and what is the best cleaner for one?
Baking soda followed by vinegar is fine as a freshener, but it lifts only a little of the film and does nothing to a wad of hair. For a drain that smells and is not clogged, the best cleaner is a scrub with dish soap and a strip pulled through, followed by an enzyme dose for upkeep. A harsh chemical opener does not remove the smell at its source, and it is hard on a tub.
What not to do: do not pour a harsh chemical opener into a drain just because it smells. Do not mix bleach with any other cleaner, and especially never with an acid or ammonia product, because the mix gives off toxic gas. If you have a septic system, the EPA advises avoiding chemical drain openers and says pouring toxins down the drain can kill the living organisms that treat the waste in the tank.
Cause two: a dried-out trap
Under the strainer is a curved section of pipe that holds a small amount of water. That water is a seal. It is the only thing between your bathroom and the sewer gas in the pipes, so the drain does not smell while it is full. Water evaporates, and a shower that sits unused in a guest room, a basement or a vacation home can lose that seal in a few weeks.
The fix is free. Run the water for a full minute and the smell usually disappears with the first flush. A university extension recommends pouring a quart of water into seldom-used drains every three to four weeks. To keep the seal in a shower that stays unused, run the water on that schedule, or after refilling the trap pour in a small amount of mineral oil. A city utility notes that mineral oil floats on the water and can slow evaporation, and that it is preferred over cooking oils because it does not go rancid and cause its own odor.
If you refill the trap and the smell returns within a day or two, the water is going somewhere. That is a sign to move to the next cause.
Cause three: a venting problem
Every drain line needs a vent, a pipe that leads up through the roof and lets air in behind the water as it flows. Without that air, the draining water pulls like a piston and can suck the water out of the trap, which opens the seal and lets gas through. The signs are a gurgle or a glugging sound as the shower drains, a slow drain that clears when you open a window, or a trap that keeps going dry even though you use the shower.
A vent can be blocked by leaves, a bird's nest or ice, or it can be missing after a remodel. In cold weather, moisture in the warm air from the sewer can freeze at the top of the vent on the roof, and a North Dakota State University extension notes the first sign is often a toilet that gurgles or does not flush properly. You can check the opening on the roof from the ground with binoculars, but climbing up to clear a vent is not a job to take on without the right gear. Vent troubles are the point where guessing stops being useful, because the pipe you need to look at is inside a wall and above the ceiling.
Cause four: sewer gas that points to something larger
Sometimes the smell is not from the shower at all. Sewer gas smells like rotten eggs, and it can come from:
Hydrogen sulfide smells like rotten eggs. The federal toxic substances agency says people lose the ability to smell it after roughly two to fifteen minutes at about 100 parts per million, which makes smell a poor warning, so a smell that seems to fade is not proof that it has gone. Longer exposure at low levels can cause eye irritation, headache and fatigue. If the odor is strong, if anyone feels unwell, or if it is in several rooms, open windows and leave the room. Our page on sewer smell in the house walks through how a smell is traced through the whole system.
If the shower also drains slowly or gurgles when the toilet flushes, you may have a main line problem and not a smell problem. In that case see sewer line backing up.
The hot water smell is a different problem
If the water itself smells like rotten eggs but only the hot side, the cause is usually in the water heater and not the drain. The Minnesota Department of Health explains that a water heater can create a warm place where sulfur bacteria live, and that the magnesium rod inside the tank (the anode) can supply electrons that help turn sulfate into hydrogen sulfide gas. To check, fill a glass at the hot tap and one at the cold tap after the house has been quiet for a few hours. If only the hot side smells, the drain is not your problem. The same page advises that unless you are very familiar with water heater maintenance, you should have a plumber or water system professional do any work on it.
Why a deodorizer does not fix it
It is tempting to drop a scented tablet or pour perfumed cleaner into the drain. That covers an odor for a day, and meanwhile the film is still growing or the trap is still dry. What to put down a drain to stop a smell is, honestly, water for a dry trap, a scrub and an enzyme maintenance dose for biofilm, and nothing at all when the cause is a vent or a pipe, because no liquid fixes those.
Why does the smell keep coming back after I clean it?
If you scrubbed the strainer, ran a strip through and refilled the trap, and the smell returns in days, the cause is almost never the part you cleaned. The remaining possibilities are a vent that keeps pulling the trap dry, a leak or crack in the pipe that lets gas out behind the wall, or a partial blockage farther down. Those are all found by looking at the pipe, and none of them are fixed by another round of cleaner.
When should I stop and call a plumber?
Call if any of these apply:
- You cleaned the strainer, scrubbed the drain, and refilled the trap, and the smell is back within a few days.
- The smell is strongest at night or in a closed bathroom and does not clear.
- More than one drain in the house smells, or the drains gurgle.
- A fixture is slow as well as smelly.
- The smell is sewage and not musty, or anyone has a headache that goes away outdoors.
The place to start is our clogged shower and tub drain page, which covers what the work involves from our side. For the wider picture see drain cleaning and, for a home on septic, septic services. If the drain is slow as well, see how to unclog a shower drain. Call (208) 366-5771.
What it costs to have us do it
Clearing a single branch line, one fixture and not a main line clog, is covered by our $59 drain cleaning special. Past that, what moves the price is which fixture is involved, whether there is a cleanout or other way in, whether the line needs a cable or jetting, and whether the trouble sits in the branch or the main. We diagnose first, then hand you a flat price in writing that you approve before anything starts. It is a flat rate and not an hourly meter, and on-site estimates are free.
Is a smelly drain dangerous?
A musty drain is a nuisance. Hydrogen sulfide, the gas in sewer gas, can irritate the eyes and cause headaches over time, so a strong sewage smell or headaches that ease outdoors are reasons to ventilate and call.
Can bleach cure a drain smell?
It can mask it, but it does not remove a film of hair and soap, and it must never be mixed with other cleaners.
Why does my shower drain smell like mildew or body odor?
That musty, sour smell is usually a film of soap, skin oil and hair that bacteria feed on in the strainer and trap. Scrubbing it out and pulling a strip through the drain removes the source.
Why does my drain smell bad even though there is no blockage?
A drain can run freely and still smell if the trap has dried out, the vent is pulling the water seal away, or the film on the pipe wall is building. The timing of the smell tells you which.
Where we work
American Rooter & Drain was established in Caldwell, Idaho in 1945 and has worked the greater Treasure Valley since 1945. We snake drains in Boise, Nampa, Caldwell, Meridian, Kuna, Eagle, Star, Middleton, Garden City, Emmett and the rest of the valley, plus Ontario, Nyssa and Vale in Oregon. See what we do in Boise, Nampa, Caldwell and Meridian. Call (208) 366-5771, days, nights, weekends and holidays.
