A washing machine drains through its hose into a standpipe in the wall or floor behind the washer, or into a laundry tub, and from there through a trap to the building drain. Standpipes are commonly 2 inches, and older ones are often 1-1/2 inches. Lint, soap scum and small items clog them: clean the washer's pump filter, auger the standpipe, and have the branch jetted if it keeps overflowing.
- The drain hose ends in a standpipe, a laundry tub or, in some older basements, near a floor drain; each has a trap before the building drain.
- A standpipe that overflows during the spin cycle is usually too small, partly clogged or poorly vented.
- Lint and soap scum are the usual culprits, and hard water makes the scum tougher.
- Many front-load washers have a pump filter that catches socks and coins; clean it before blaming the drain.
- A floor drain that rises when the washer empties points to the building drain, not the laundry pipe.
01 /Where is the washing machine drain pipe?
Follow the grey or black drain hose from the back of the washer. It ends in one of a few places, and each has a trap between it and the building drain.
| Setup | What to look for | Common in |
|---|---|---|
| Standpipe in a washer box | A recessed box in the wall behind the washer holding the hot and cold taps and an open drain pipe | Newer and renovated laundry rooms |
| Freestanding standpipe | An open vertical pipe rising from the floor or along a wall near the washer | Basements and older laundry areas |
| Laundry tub | The hose hooks over the edge of a utility sink, which drains through its own trap | Many older Canadian basements |
| Near a floor drain | The hose runs to or toward a basement floor drain | Some older basements; an arrangement that may not meet current rules |
In every setup, the hose end should sit loosely in the standpipe or tub, not sealed into it. That gap lets air in, so the drain cannot siphon dirty water back toward the washer. It is also why taping a hose tightly into a standpipe to stop splashing is a mistake.
02 /What size should a washing machine drain pipe be?
Many newer installations use a 2-inch (50 mm) standpipe and trap, and older laundry areas often have 1-1/2-inch (38 mm) pipe. Modern washers pump out quickly, and a smaller or partly restricted standpipe is the most common reason for water spilling over the top during the drain cycle. Your provincial plumbing code sets the minimum size and the standpipe rules, so confirm them before changing anything.
| Check | Why it matters |
|---|---|
| Standpipe diameter | Larger pipe accepts a fast pump-out with less risk of overflowing |
| Standpipe height above the trap | Too short can overflow or siphon; too tall can exceed what the washer pump can lift. The washer manual states a drain-height range, and the code sets minimum and maximum heights |
| How far the hose goes in | Pushed too deep, the hose can siphon; follow the washer manual |
| Trap and vent | A standpipe without proper venting gurgles, drains slowly and can pull water from other traps |
| Distance to the stack or building drain | Long, flat branches collect lint and scum faster |
03 /What clogs a washing machine drain?
Laundry drains clog with material that comes off clothes and out of detergent. Each culprit leaves a clue.
| Culprit | Where it collects | The clue |
|---|---|---|
| Lint and fibres | The standpipe trap and branch | A grey, felt-like mat on an auger |
| Soap scum and fabric softener residue | Pipe walls, worse in hard water | A waxy grey coating |
| Pet hair | The trap and the washer's pump filter | Hair mats |
| Socks, coins and hair ties | The pump filter, hose or trap | The washer drains slowly or shows a drain error |
| Sand and grit | The trap and building drain | Gritty sludge after work, beach or ski clothes |
| A partly blocked building drain | Downstream of the laundry | The floor drain rises when the washer empties |
Hard water turns detergent into stickier scum that binds lint; see hard water scale in drain pipes. Using the recommended amount of detergent, rather than extra, cuts down the residue that ends up in the pipe.
04 /How do you clean a washing machine drain pipe?
- Start with the washer
Unplug it. On many front-loaders, a pump filter sits behind a small door near the bottom front; drain the water into a shallow pan and towel, then remove socks, coins and lint. Check the drain hose for kinks and for a lint plug at the end.
- Look into the standpipe
Pull the hose out and shine a flashlight down the standpipe. Lint near the top can be pulled out by hand with a glove.
- Auger the standpipe
Feed a 1/4 or 5/16 inch hand auger down the standpipe, through the trap and into the branch. Lint wraps around the cable, so retrieve it slowly with a rag ready.
- Test with a bucket
Pour a full bucket of hot tap water down quickly. If the standpipe rises close to the top, it is still restricted.
- Clean the laundry tub trap
If the washer drains into a tub, clean that trap the same way as a sink trap.
- Add a lint catcher
A mesh lint trap on the hose end in a laundry tub catches fibres before they reach the drain; empty it every load or two.
- Jet the branch if it keeps coming back
A laundry line that overflows every few months usually has a scum layer along its length that an auger only punctures. Jetting cleans the full wall.
05 /How do you clean the pipes inside a washing machine?
The washer's own tub, hoses and seals collect detergent residue, lint and bacteria that cause odours. Cleaning them is separate from cleaning the house drain, and the washer's manual is the authority.
- Run the manufacturer's cleaning cycle, or an empty hot cycle, with a washer cleaner or the product the manual approves.
- On front-loaders, wipe the door gasket and the folds behind it, where water and lint sit.
- Clean the pump filter on a schedule, not only when the washer complains.
- Leave the door or lid open between loads so the drum dries.
- Do not put bleach and vinegar into the same cycle, or run them back to back without a rinse in between; together they release chlorine gas.
For which household products are safe to combine, see bleach, peroxide and solvents in drains.
06 /Why does the floor drain back up when the washer drains?
When the basement floor drain rises while the washer empties, the laundry pipe is usually fine. A washer sends a large volume of water in a short time. If the building drain or lateral downstream is partly blocked, that water backs up to the lowest opening in the house, which is the floor drain.
- Stop doing laundry
Every load pushes more water toward the blockage, and the next one may flood the floor.
- Stop other water use
Toilets, showers and the dishwasher all feed the same building drain.
- Have the building drain augered from a cleanout
That restores flow and shows what is causing the blockage.
- Camera the line
Repeated laundry-day backups often mean roots, a sag or scale in the building drain or lateral.
The method that follows depends on what the camera finds; see pipe cleaning methods compared and DIY vs professional pipe cleaning. If a toilet gurgles whenever the washer drains, venting may also be involved; see main stack and vent cleaning.
07 /What does laundry drain cleaning cost?
| Item or service | Typical range |
|---|---|
| Mesh lint trap for the hose | $5 to $20 |
| Standpipe or laundry branch augered | $150 to $350 |
| Laundry branch jetted | $300 to $650 |
| Building drain augered from a cleanout | $200 to $450 |
Check the method for your house with the Pipe Method Matcher, or request quotes that name jetting if the branch keeps overflowing. For setting an interval on a line that keeps coming back, see how often to clean drain pipes.
FAQQuestions people ask
What size drain pipe does a washing machine need?
Many newer installations use a 2-inch standpipe and trap, and older ones are often 1-1/2 inches. Smaller pipe is more likely to overflow with a fast-pumping washer. Your provincial plumbing code sets the minimum; confirm before replacing it.
Where does the washing machine drain go?
Through its hose into a standpipe or a laundry tub, then through a trap into a branch drain and on to the building drain and the sewer.
Why does my washing machine drain overflow?
The standpipe is taking water more slowly than the washer pumps it. Common causes are lint or scum in the trap or branch, a standpipe that is too small or short, poor venting, or a blockage further down the building drain.
Can I use a chemical drain cleaner in a washer standpipe?
It is not recommended. The chemical sits in the trap, rarely clears lint and scum, and can splash when the hose is removed or the line is augered. Mechanical cleaning is safer and works better.
Why does the toilet gurgle on laundry day?
A large pulse of water pulls air through the easiest path. If the vent is restricted or the drain partly blocked, that air comes through the toilet trap. Have the vent and drain checked.
How do I stop lint from clogging the drain?
Clean the washer's pump filter regularly, fit a mesh lint trap where the hose drains into a laundry tub, use the recommended amount of detergent, and have a chronically slow branch jetted.
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