Short answer: Nine times out of ten, a slow or standing-water shower is hair tangled with soap scum just below the drain cover. Remove the cover, pull the hair out with a plastic drain tool or a bent wire, and flush with hot water. If the shower drains slowly with no hair, or the toilet and other drains are slow too, the clog is further down.
Quick diagnosis
What you notice
Most likely cause
What to check
Call a pro?
Water pools during a shower, drains after
Hair and soap near the drain
Remove the cover and look
Rarely
Standing water that will not drain
Hair mat or object in the trap
Plunge with the overflow (tub) covered
If it will not clear
Slow but no hair visible
Soap scum and buildup in the trap
Hand snake into the trap
Sometimes
Shower and toilet both slow or gurgling
Branch or main line clog
Check other drains
Yes
Clog came back right after Drano
Chemical softened but did not remove the mat
Use a mechanical tool
If it persists
How to clear a shower drain
Remove the drain cover (pop-out, twist-off or two screws).
Use a plastic barbed drain tool or a bent wire hanger to pull out hair.
Run hot water for a minute.
If it is still slow, plunge: fill a little water, seal the plunger over the drain and, for tubs, cover the overflow plate with a wet rag.
Still slow? A small hand snake can reach the trap.
Why it keeps clogging
Long hair and bar soap combine into a sticky mat. A hair catcher over the drain is the cheapest prevention, and cleaning it weekly keeps the trap clear. Repeated chemical cleaners can damage older pipes and are dangerous if they splash back during plunging.
When to call a professional
Water backs up into the shower when you flush the toilet or run the washer.
More than one fixture is slow.
You cannot remove the drain cover or the pipe is damaged.
What it usually costs
Clearing a drain typically costs about $100 to $275 with a plumber, according to HomeGuide (2026). A plastic drain tool or a hair catcher costs a few dollars.
Frequently asked questions
Why does my shower drain slowly even with no hair?
Soap scum and mineral buildup can narrow the trap, or the clog is further down the branch line.
Why does water come up in my shower when I flush?
The toilet and shower share a drain line further down. Water backing up into the shower points to a clog in that shared line or in the main sewer line.
Short answer: If the disposal hums but does not spin, it is jammed: turn it off, free it with a 1/4-inch hex (Allen) wrench in the bottom center socket, press the red reset button and try again. If it makes no sound at all, press the reset button, wait, and check the breaker. Never put your hand in the disposal.
Quick diagnosis
What you notice
Most likely cause
What to check
Call a pro?
Hums but does not spin
Jammed flywheel
Turn the bottom hex socket with an Allen wrench
If it will not free
No sound at all
Overload protector tripped, or no power
Press the red reset button under the unit
If power is fine and it still is dead
Runs but sink does not drain
Clog in the drain line past the disposal
Check the other sink side and the trap
Sometimes
Stops after a few seconds
Motor overheating or partial jam
Free the jam, let it cool 10 to 20 minutes
If it repeats
Leaks from the bottom
Internal seal failure
Look under the unit with a flashlight
Usually means replacement
Hums but does not turn (jammed)
InSinkErator, the largest disposal manufacturer, gives these steps for most of its models:
Turn the disposal switch off. Never put your hand inside the unit.
Insert the Jam-Buster wrench or a standard 1/4-inch Allen wrench into the hole at the bottom center of the unit, under the sink.
Work it back and forth until it turns freely in full circles.
Press the small red reset button on the bottom. If it will not stay in, wait ten minutes and try again.
Look into the chamber with a flashlight and remove any object with tongs or pliers.
Run cold water and turn the disposal on.
No sound at all
The motor has an overload protector that trips when it overheats or jams. Press the red reset button. If nothing happens, InSinkErator suggests letting the unit cool for up to 20 minutes and then checking your breaker panel for a tripped breaker or blown fuse. Models with an air switch on the countertop should be unplugged for the same cooling time.
Runs but the sink will not drain
If the motor runs normally, the clog is in the drain pipe after the disposal or in the trap. See kitchen sink clogged.
When to call a professional
The motor stays silent after reset and the breaker is on.
The unit leaks from the bottom or the body.
It keeps tripping the reset button or the breaker.
You see scorch marks, smell burning or hear electrical buzzing.
What it usually costs
Freeing a jam costs nothing if you have an Allen wrench. A plumber visit typically starts with a call-out fee and $45 to $150 per hour, according to HomeGuide (2026).
Frequently asked questions
Where is the reset button on a garbage disposal?
On most models it is a small red or black button on the bottom of the unit, under the sink.
Why does my disposal hum and not turn?
Something is wedged between the turntable and the grinding ring. Turning the hex socket at the bottom frees it.
Short answer: A clog is likely deep in the pipe when plunging and cleaning the trap do nothing, when more than one fixture is slow, or when water comes up in a tub or floor drain as you flush. One fixture: the branch line. Several fixtures, especially on the lowest floor: the main sewer line, which needs a plumber.
Quick diagnosis
What you notice
Most likely cause
What to check
Call a pro?
One sink slow, trap is clear
Clog in that branch line
Hand snake into the wall pipe
If the snake will not clear it
Toilet flush makes tub or shower gurgle or back up
Main line partly blocked
Watch the lowest drain while flushing
Yes
All drains slow, smell in basement
Main sewer line blockage or break
Check the cleanout area
Yes
Clogs return every few months
Roots, sagging pipe or grease buildup
Note how often it happens
Yes, camera inspection
Branch line vs main line
Each fixture drains into a branch pipe, and branches join the main line that leaves the house. A clog in a branch affects one fixture or one room. A clog in the main line affects everything downstream, which is why the lowest fixtures (basement drains, first-floor tubs) back up first.
What you can safely try
A hand snake through the fixture or the trap arm for a single slow drain.
Stop running water in the house if water is backing up into tubs or floor drains.
Avoid chemical cleaners for deep clogs; they rarely reach and can make the plumber’s job dangerous.
What a plumber does
A plumber clears main line clogs with a powered auger through the cleanout, and can run a camera to see roots, breaks or belly (sagging) sections. Recurring clogs are worth a camera inspection before paying for repeated cleanings.
When to call a professional
More than one drain is slow or backs up.
Sewage appears in a tub, shower or floor drain.
Clogs keep coming back.
You notice wet spots or sinkholes in the yard along the sewer line.
What it usually costs
HomeGuide (2026) lists sewer line cleaning at about $150 to $800 and a sewer camera inspection at about $125 to $500.
Frequently asked questions
How do I know if my main sewer line is clogged?
Several drains slow at once, gurgling, and water backing up into the lowest drains when you flush are the classic signs.
Can I snake a main line myself?
Renting a powered auger is possible, but it can damage pipes or get stuck. For main lines, most homeowners are better off with a plumber.
Short answer: Most kitchen clogs are grease, coffee grounds and food scraps stuck in the P-trap or in the pipe inside the wall. If only one side of a double sink is slow, the clog is in that side or the disposal. If both sides are backed up and the P-trap is clear, the clog is further down the line and a drain snake or a plumber is the next step.
Quick diagnosis
What you notice
Most likely cause
What to check
Call a pro?
One side slow, the side with the disposal
Disposal jammed or drain outlet clogged
Run the disposal; check for humming
Rarely
Both sides backed up
Clog in the shared trap or branch line
Remove and check the P-trap
If past the trap
P-trap is clear but water still backs up
Clog in the pipe inside the wall
Use a hand snake through the wall pipe
Often
Kitchen and other drains slow
Main line problem
Check other sinks and toilets
Yes
Dishwasher water backs into the sink
Clog in the sink drain or disposal
Clear the sink drain first
If it continues
What to try first
Turn off the disposal and the dishwasher.
Use a cup plunger on the clogged side; if you have a double sink, cover the other drain with a wet rag or a stopper so the pressure goes to the clog.
Run hot water for a minute; it can loosen grease, but do not pour boiling water into a sink full of standing water or into plastic pipes repeatedly.
Put a bucket under the trap, loosen the two slip nuts by hand and remove the curved section. Clean it out and reinstall it, making sure the washers sit correctly so it does not leak or smell. If the trap was clear, the clog is in the pipe beyond it.
Clog past the P-trap
A hand snake (drain auger) fed into the pipe going into the wall can reach clogs a few feet away. If that does not work, or if other drains are also slow, the problem is further down and a plumber should clear it. Avoid mixing chemical drain cleaners with a plunger or a snake: splashing drain cleaner causes burns.
When to call a professional
Water does not go down after plunging and clearing the trap.
Other drains in the house are slow or gurgle.
You have already used a chemical drain cleaner (tell the plumber).
The pipe under the sink leaks or is corroded.
What it usually costs
HomeGuide (2026) lists unclogging a drain at about $100 to $275 and plumbers at $45 to $150 per hour, plus a call-out fee in many areas.
Frequently asked questions
Why are both sides of my kitchen sink clogged?
Both sides drain into the same pipe. If both are backed up, the clog is in the shared part of the trap or further down the branch line.
Does baking soda and vinegar unclog a drain?
It can help with light buildup and odors, but it rarely clears a real grease or food clog. Mechanical methods (plunger, trap cleaning, snake) work better.
Short answer: Most sewer smells come from sewer gas getting past a plumbing seal. The usual suspects, in order: a dry P-trap in a drain you rarely use (basement floor drain, guest shower, laundry standpipe), a toilet with a failed wax ring, a blocked or damaged roof vent, and a cracked or backed-up sewer line. If the smell is strong, comes with gurgling drains or backups, or makes you feel sick, ventilate the house and call a plumber.
Quick diagnosis
What you notice
Most likely cause
What to check
Call a pro?
Smell near a floor drain or unused shower
Dry P-trap (the water seal evaporated)
Pour a few quarts of water into the drain
Only if refilling does not help
Smell around the base of one toilet, maybe a wobble
Failed wax ring or loose toilet
Rock the toilet gently; look for water at the base
Yes, if you are not comfortable resetting a toilet
Smell when it rains or when fixtures drain, gurgling sinks
Blocked or damaged plumbing vent
Listen for gurgling when the tub or washer drains
Yes (roof work)
Smell plus slow drains in several fixtures
Partial blockage in the main sewer line
Check whether more than one drain is slow
Yes
Rotten-egg smell only from hot water taps
Water heater reaction, not sewage
Compare hot and cold water at the same tap
See our water heater guide
Smell under a sink, in a cabinet or wall
Loose slip joint, cracked pipe or open pipe
Look and sniff under sinks with a flashlight
If the leak is in a wall
1. A dry P-trap (the most common cause)
Every drain has a curved pipe, the P-trap, that holds a little water. That water is the seal that keeps sewer gas out of the room. In a drain that is rarely used, such as a basement floor drain, a guest bathroom shower or a laundry standpipe, the water slowly evaporates and the gas comes straight in.
Oatey, a plumbing products manufacturer, lists dry traps first among the causes of sewer gas odor and recommends running water through unused drains regularly, about a gallon a month.
Pour two to three quarts of water into every drain you do not use often, including floor drains.
Wait an hour. If the smell fades, the trap was dry.
For drains that dry out again quickly, a little mineral oil on top of the water slows evaporation, or a one-way drain seal sized to the pipe can be installed.
2. A toilet that is not sealed
Toilets have no visible trap under the floor. The seal is a wax ring between the toilet and the floor flange. If the toilet rocks, was recently reset, or the flange sits too low, sewer gas can leak around the base.
Signs: the smell is strongest near one toilet, the toilet moves when you sit, or you see staining or water at the base. Replacing the wax ring means removing the toilet; many homeowners do it, but if the flange is broken or the floor is soft, it is a job for a plumber.
3. A blocked or damaged plumbing vent
Vent pipes run from the drain lines up through the roof. They let air into the system so that water flowing down a drain does not suck the water out of nearby traps. Leaves, nests, snow or a disconnected pipe in the attic can block or break a vent.
Typical clues: sinks or tubs gurgle when another fixture drains, the smell shows up when the washing machine empties or during windy or rainy weather, and traps keep losing their water even though the drains are used. Clearing a roof vent means working on the roof, so most people call a plumber or roofer.
4. A problem in the main sewer line
If several drains are slow, a floor drain or tub backs up when you flush or run the washer, or the smell is worst near the basement cleanout, the main line may be partly blocked by roots, grease or a broken pipe. This is the cause that gets worse and more expensive if it waits.
A plumber can run a camera through the line to see what is inside. Sewage backups are a health hazard: keep people and pets away from the water and do not try to clean up a backup without protection.
5. Other places the smell can come from
Sink overflow holes: soap and gunk in the overflow channel of a bathroom sink can smell like sewage. Clean it with a bottle brush and hot water.
Loose or open pipes: a slip nut under a sink that worked loose, or an old drain pipe that was left open or stuffed with a rag during a remodel.
Hot water only: a rotten-egg smell that only comes from hot taps is usually the water heater, not the sewer. See hot water smells like rotten eggs.
Not plumbing at all: natural gas has a rotten-egg odor added on purpose. If you think it could be gas, leave the house and call your gas utility from outside.
Smell only when it rains, after a shower or when doing laundry
When it rains: pressure changes and heavy flow in the sewer can push gas past weak seals, and a blocked vent makes this worse. Check vents and floor drains first.
After a shower or doing laundry: a large volume of water draining at once can siphon nearby traps when venting is poor. Gurgling at the same moment is the giveaway.
Comes and goes: traps that slowly dry out between uses, or a vent issue that depends on wind and weather.
When to call a professional
The smell is strong, makes anyone dizzy or sick, or you cannot find the source.
Sewage or dirty water comes up in a tub, shower or floor drain.
More than one drain is slow or gurgles.
You suspect a roof vent problem or a cracked pipe inside a wall or under a slab.
You smell something like gas: leave first, then call the gas utility.
What it usually costs
Refilling a dry trap costs nothing. HomeGuide (2026) lists most plumbers at $45 to $150 per hour, with call-out fees usually $50 to $200. Clearing a clogged drain runs about $100 to $275, sewer line cleaning about $150 to $800, and a sewer camera inspection about $125 to $500. Prices vary a lot by region.
Frequently asked questions
Is sewer gas dangerous?
In the small amounts that usually cause a household smell, the main issue is the odor and what it says about your plumbing. Higher concentrations can cause headaches, nausea and dizziness, and sewer gas can contain methane. Ventilate, find the source and get it fixed.
How do I know if it is a dry trap?
Pour water into the drain you suspect. If the smell fades within an hour or so, the trap was dry. Rarely used floor drains and guest showers are the usual culprits.
Why does my house smell like sewage but there is no leak?
Gas can escape through a dry trap, a loose toilet seal or a blocked vent without any water leaking. The smell itself is the sign of a broken seal somewhere in the system.
Short answer: In a bathroom, check four things in this order: the shower or tub drain (dry or dirty trap), the sink overflow hole, the toilet seal at the floor, and the vent. If the smell comes and goes with flushing or with other fixtures draining, a venting problem is likely and a plumber should look at it.
Quick diagnosis
What you notice
Most likely cause
What to check
Call a pro?
Smell from the shower drain, guest bath
Dry trap or hair and soap buildup
Run water for a minute; clean the drain
Rarely
Smell from the sink
Dirty overflow channel or P-trap
Clean the overflow hole with a brush
Rarely
Smell at the base of the toilet
Failed wax ring or loose bolts
Gently rock the toilet; check for water at the base
Often
Smell after flushing or when the tub drains, gurgling
Vent problem siphoning traps
Listen for gurgling in other fixtures
Yes
Smell comes and goes
Trap slowly drying, or weather-related venting
Note when it happens
If it continues
Step-by-step: find the source
Run water in the shower, tub and sink for a minute each to refill the traps.
Clean the sink overflow hole with a bottle brush and hot water; gunk in the overflow often smells like sewage.
Sniff around the toilet base. If it rocks or the caulk is stained, the wax ring is a prime suspect.
Flush the toilet and drain the tub while listening to the sink. Gurgling means air is being pulled through the trap, which points to a vent problem.
Check the exhaust fan works; a bathroom with no ventilation holds odors longer.
The toilet wax ring
The wax ring seals the toilet to the drain flange. It can fail after the toilet is moved, if the bolts loosen, or when the flange is set too low, according to Oatey. Replacing it means shutting off the water, draining the toilet and lifting it. If the flange is cracked or the subfloor is soft, call a plumber.
Venting problems
A blocked or undersized vent lets a draining fixture pull the water out of other traps in the bathroom. The tell-tale signs are gurgling and a smell right after a flush or after the tub drains. Fixing it can involve the roof vent or adding an air admittance valve, which a plumber should handle.
When to call a professional
The toilet rocks, the floor around it is soft, or water appears at the base.
Fixtures gurgle when others drain.
The smell continues after refilling traps and cleaning drains.
Sewage backs up into the tub or shower.
What it usually costs
Cleaning drains and refilling traps is free. A plumber typically charges $45 to $150 per hour plus a call-out fee, and toilet repairs commonly run $100 to $300, according to HomeGuide (2026).
Frequently asked questions
Why does my bathroom smell like sewer only sometimes?
The smell that comes and goes is usually a trap that slowly dries out or a vent problem that depends on how much water is draining or on the weather.
Can a bathroom sink overflow smell like sewage?
Yes. Soap scum, hair and bacteria collect in the overflow channel and can smell like sewer gas. Cleaning it often solves the problem.
Short answer: Start with the floor drain: pour a few quarts of water into it, because a dry trap is the most common cause. Then check the cleanout cap, the laundry standpipe and any sewage ejector pit. If the smell gets worse after heavy rain or water comes up through the floor drain, the main sewer line or the city sewer may be overloaded, and you should call a plumber.
Quick diagnosis
What you notice
Most likely cause
What to check
Call a pro?
Smell near the floor drain
Dry trap
Pour water into the drain
Only if it keeps drying out
Smell near a capped pipe on the wall or floor
Loose or missing cleanout cap
Check the cap is tight and present
If damaged
Smell near a covered pit
Sewage ejector pit lid not sealed
Check the lid and its gasket
Often
Worse after heavy rain, water at the drain
Overloaded or blocked sewer line
Watch the floor drain during rain
Yes
Musty smell, not sewage
Damp basement, mold
Look for water stains and humidity
Depends
Dry floor drain traps
Basement floor drains are often used only a few times a year, so their traps dry out. Oatey recommends running water through unused drains about once a month, and a drain seal can keep gas out between uses.
Cleanouts and ejector pits
A cleanout is a capped opening on the drain line used to clear clogs. If the cap is missing, cracked or loose, gas escapes. Homes with a basement bathroom often have a sewage ejector pit with a sealed lid; if the lid or its gasket is not tight, the basement will smell.
Smell after heavy rain
Heavy rain can overload combined or aging sewer systems and push gas, and sometimes water, back toward the house. A partially blocked main line makes this worse. If dirty water rises from the floor drain, stop using water in the house and call a plumber. Ask about a camera inspection and whether a backwater valve makes sense for your home.
When to call a professional
Water or sewage comes up through a floor drain.
The smell is strong or you feel unwell.
A sewage ejector pump runs constantly or alarms.
Several drains in the house are slow.
What it usually costs
HomeGuide (2026) lists sewer line cleaning at about $150 to $800 and sewer camera inspections at about $125 to $500. Plumbers typically charge $45 to $150 per hour plus a call-out fee.
Frequently asked questions
Why does my basement smell like sewage after it rains?
Rain can overload the sewer system and push gas back through weak seals, especially a dry floor drain or a partly blocked main line.
Is a floor drain smell dangerous?
A faint smell from a dry trap is mainly a nuisance, but strong or persistent sewer gas should be dealt with, and any sewage backup is a health hazard.