Plumbing · Drains
Clogged Drain? Causes and How to Clear It
Clogged drain? First check whether one drain or several are slow. Then clean the stopper, plunge, open the trap or use an auger, and when to call a pro.
Quick answer
If one sink, tub or shower is slow, the clog is usually close: hair on the stopper, gunk in the trap, or a plug a plunger or auger can reach. If several drains back up at once, the main line is blocked; call a plumber. Skip chemical drain openers on a fully blocked drain.
- Time to fix
- 10–90 min
- Difficulty
- Easy, 1 of 4
- Safety
- Warning
On this page · 10 sections
A clogged drain is either a local problem or a whole-house one, and the fix depends on which. Simsbury, Connecticut's sewer department puts it plainly: all drains backing up at once points to the main sewer line, not a single fixture.[1] When only one sink, tub or shower is slow, the clog is usually close to it; UF IFAS Extension says most sink clogs are in the trap.[2] This guide starts with that check, then works through the local fixes from the least effort to the most. For how traps and drain lines fit together, see how drains and traps work.
Before you start
Shut-offs
Water
Turn the faucet off. For a sink, the shutoff valves under it stop water if a faucet will not close.
Put on rubber gloves. Drain water carries food, soap and hair, and backed-up sewage is a health risk. Fargo's water department says to avoid contact with sewage.[4]
You'll need
- Nitrile-coated work gloves
- 5-gallon bucket
- Microfiber towels
- Adjustable wrench
- LED work flashlight
Why the drain is clogged
Start with the first cause and stop when the water runs freely.
Overflow hole DIY
The hole near the rim of a bathroom sink drains into the pipe below the stopper. Plug it with a wet rag before you plunge, so the pressure goes to the clog. On a double kitchen sink, plug the other drain.[2][6] Plunge the drain: Overflow hole
Stopper and strainer DIY
Hair and soap build up on the stopper of a bathroom sink, tub or shower; a kitchen strainer catches food. UF IFAS Extension says to clean the hair out of the drain after you wash your hair.[2][6] Clean the stopper: Stopper and strainer
Trap (P-trap) DIY
The U-shaped bend of pipe under the sink. UF IFAS Extension says most sink clogs are in the trap, so it is the first pipe to open when plunging fails.[2] Clean out the trap: Trap (P-trap)
Water seal DIY
The water that stays in the trap is a barrier against sewer gas. A drain you rarely use can dry out and smell; Phoenix Water Services refills the trap with about a quart of water.[9]
Cleanout plug DIY
Some traps have a plug at the bottom. UF IFAS Extension sets a pan or bucket under the trap and unscrews the plug with an adjustable wrench to reach the clog.[2]
Vent pipe Pro only
All drain plumbing is vented. The vent pipe runs up inside the wall and out the roof. A cracked vent or a bad joint can leak sewer gas; a plumber can find it with a smoke test.[9]
Branch drain and main line Pro only
Past the trap, the drain joins the other fixtures and leaves the house as one pipe, the lateral, which the owner must maintain. All drains backing up at once points to the main line, not one fixture.[1] When other drains are slow: Branch drain and main line
- Kitchen sinks. A kitchen drain can also take a second basin, a disposer or a dishwasher air gap. Korky blocks each of those openings before plunging.[6]
Blockage in the main sewer line
Several drains are slow or back up at the same time.What a pro does: Blockage in the main sewer lineHair and soap on the stopper or strainer
A bathroom sink, tub or shower drains slowly.Fix it: Hair and soap on the stopper or strainerClog just below the drain opening
The fixture holds water and gurgles.Fix it: Clog just below the drain openingGrease, food or debris in the trap
Plunging moves the water but it backs up again.Fix it: Grease, food or debris in the trapClog past the trap
The trap is clean but the drain is still blocked.Fix it: Clog past the trap
| What you see | Where the clog likely is | First step |
|---|---|---|
| Only one fixture is slow | Stopper, strainer or trap[2] | Clean the stopper, then plunge |
| Toilet flush backs up the shower or tub | Main sewer line[4] | Stop using water; call a plumber |
| Water comes up a basement floor drain | Main sewer line[1] | Stop using water; call the utility or a plumber |
| Kitchen sink with a disposer swirls but won't drain | Drain line below the disposer[5] | See the kitchen sink guide |
| Dishwasher leaves water in its tub | The sink drain it shares through the air gap[6] | Clear the sink drain first |
| Water drains, then gurgles and smells of sewage | Main line or sewer[1] | Call the utility or a plumber |
Check whether other drains are slow
Fargo's water department lists the signs of a sewer blockage: slow fixtures, several fixtures backing up at once, and one fixture affecting another, such as a flushing toilet that backs sewage up into the shower.[4] Simsbury adds gurgling, sewage smells and water coming up through tubs, toilets or basement floor drains.[1]
Run water in a second fixture
- Time: 3 min
Run a nearby sink or tub for a minute and watch the toilet, the tub and any floor drain.[4]
You'll know it worked when: You know whether the problem is one drain or the whole house.
Stop all water use if more than one drain backs up
- Time: 1 min
Every flush and every shower adds to the backup.
You'll know it worked when: No more water goes into the blocked line.
Call the sewer utility or a plumber
- Time: 5 min
Simsbury's sewer department can find where a blockage is. It says the pipes inside the house and the lateral to the main belong to the owner, and lateral repairs need a licensed plumber.[1]
You'll know it worked when: Someone is booked to find and clear the blockage.
Fargo lists the usual causes of main-line clogs: built-up grease, objects flushed down toilets, tree roots in broken pipes, and "flushables" that do not break down.[4] More is in sewer line clogged.
Still not fixed? Next likely cause: Hair and soap on the stopper or strainer
Clean the stopper and strainer
Bathroom sinks, tubs and showers collect hair and soap right at the opening. UF IFAS Extension says to clean the hair out of the drain after washing your hair.[2]
Lift out the stopper or strainer
- Time: 5 min
How the stopper comes out depends on the model. On tubs with a trip lever, UF lifts the drain cover out of the tub.[2]
You'll know it worked when: The stopper is out and you can see into the drain.
Pull the hair and soap off
- Time: 5 min
- Nitrile-coated work gloves
Wipe the stopper and reach in only as far as you can see.
You'll know it worked when: The stopper and the opening are clean.
Clean the overflow linkage on a tub
- Time: 10 min
UF removes the two screws on the overflow cover and cleans the coil on the rod, which collects hair, soap scum and body oils.[2]
You'll know it worked when: The coil on the tub's overflow rod is clean.
Run water to test
- Time: 2 min
If it is still slow, plunge next.[2]
You'll know it worked when: The water drains at a normal rate.
If a shower is still slow after this, see shower not draining.
Still not fixed? Next likely cause: Clog just below the drain opening
Plunge the drain
Use a cup plunger, the flat kind. Korky says a cup plunger is made for flat drains such as sinks and tubs; the flange plunger is for toilets.[7] Korky says a tight seal directs the pressure toward the clog, so every other opening on the drain has to be blocked.[6]
Plug the overflow and any second drain
- Time: 2 min
UF plugs the overflow on a single sink and the other drain on a double sink.[2] Korky also wraps the dishwasher air gap, if there is one, with a wet rag.[6]
You'll know it worked when: Every other opening on the drain is blocked with a wet rag or stopper.
Cover the plunger cup with water
- Time: 1 min
Korky adds enough water to cover the bottom of the plunger head.[6] For a tub, UF fills to about 2 inches.[2]
You'll know it worked when: An inch or so of water sits over the drain.
Plunge in short bursts
- Time: 5 min
UF presses down smoothly and jerks up sharply, 20 to 30 times.[2] Korky plunges for about 10 to 15 seconds, then checks and repeats. On a sink with a pop-up stopper, Korky holds the lift rod down so the stopper does not close the drain while you plunge.[6]
You'll know it worked when: The water rushes down when you lift the plunger.
Flush the drain with hot water
- Time: 3 min
UF rinses with hot, soapy water.[2] Korky runs hot water for a few minutes to wash away loosened debris.[6]
You'll know it worked when: The drain stays clear with the tap running.
Never plunge a drain that has chemical drain opener in it. Oregon State's extension sheet says so plainly.[8]
Still not fixed? Next likely cause: Grease, food or debris in the trap
Clean out the trap
The trap is the U-shaped pipe under a sink. UF IFAS Extension says most clogs are in the trap.[2]
Set a bucket under the trap
- Time: 2 min
- 5-gallon bucket
- Microfiber towels
Water and debris come out of the trap when you open it.
You'll know it worked when: A bucket catches anything that drains out.
Open the cleanout plug or the trap
- Time: 10 min
- Adjustable wrench
UF unscrews the cleanout plug at the bottom of the trap with an adjustable wrench, if the trap has one.[2] Oregon State removes the trap to clean it when plunging fails.[8]
You'll know it worked when: The trap is open over the bucket.
Pull out the clog
- Time: 5 min
- Nitrile-coated work gloves
UF uses a finger, a pencil or a wire.[2]
You'll know it worked when: The trap is clear when you look through it.
Put it back and run hot, soapy water
- Time: 10 min
- LED work flashlight
Refit the plug or trap and run water.[2] Check the joints with a flashlight for drips.
You'll know it worked when: The drain runs freely and the trap joints stay dry.
If a trap joint drips after you put it back, see sink drain pipe leaking.
Still not fixed? Next likely cause: Clog past the trap
Run a hand auger past the trap
When the trap is clean but the drain still holds water, the clog is further along the pipe. Oregon State's extension sheet uses a cleanout auger, or snake, at this point.[8]
Feed the cable in through the trap opening
- Time: 10 min
- 5-gallon bucket
Oregon State says the auger cable usually will not go down the drain opening and has to go in at the trap.[8]
You'll know it worked when: The cable is in the drainpipe past the trap.
Twist and push toward the clog
- Time: 15 min
- Nitrile-coated work gloves
Use a thrusting and twisting action. If the cable hits an obstruction, work it back and forth while twisting the handle close to the pipe opening.[8]
You'll know it worked when: You feel the cable catch or break through.
Pull the cable and put the trap back
- Time: 10 min
Once water will run through, pull the cable, refit the trap and flush the drain well with water.[8]
You'll know it worked when: The trap is reassembled and the drain runs.
If the auger cannot reach or clear it, call a plumber. UF's sheet already sends you to one when the plunger and the trap have not cleared the sink.[2]
Still not fixed? See when to call a pro
When to call a pro
Call a plumber or your sewer utility when the blockage is past the fixture or keeps coming back.
Tell the plumber which drains are affected and what you put down them, including any chemicals. If only the dishwasher backs up, see why a dishwasher holds water first.
Frequently asked questions
FAQ
Are chemical drain cleaners safe to use?
Does baking soda and vinegar unclog a drain?
How do I keep drains from clogging?
Who pays to fix a clogged sewer line?
Sources
“If You Have a Plumbing Blockage” · accessed
“Making Simple Repairs: Clogged Drains (FCS5234-05)” · PDF · pp. 1-2; archival copy, revised December 2005 · accessed
“Property Owner Responsibility” · accessed
“Clogged Garbage Disposal” · accessed
“How to Plunge a Sink” · accessed
“Sink Plunger vs Toilet Plunger Q&A” · accessed
“Fact Sheet 192: Home Plumbing” · p. 1, Clogged Drains; January 1973 · accessed
“Guidance Supplement 9: Sewer Odors in a Building or House” · PDF · accessed
How this guide was made
This guide was drafted with AI assistance from the manufacturer and safety sources listed above, then checked against those sources in an AI-assisted review. No licensed technician reviewed it. Last reviewed . Our methodology