Floor drain overflows when washer drains

Quick Answer:

Most often this is caused by lint and soap building up in the washer standpipe or the nearby floor drain, not a broken main sewer line. Start with simple checks: run a short test wash while watching the drain, clear the grate and any visible lint, check the washer hose and standpipe, and test flow from the nearest cleanout. If the problem happens only during the washer cycle, it’s usually a localized clog. If other fixtures back up, the issue may be farther down the line or in the main sewer.

Why This Happens

Washing machines send a large volume of water mixed with lint, fibers and soap into a short vertical pipe called the standpipe. If lint and soap form a soft blockage there or in the floor drain, the wash cycle can push water back up and over the drain. You may also see overflow if the drain is partially blocked downstream or if the washer discharge hose is kinked or too low into the standpipe.

Step-by-Step What to Do

1. Run a single short wash while watching the drain

Start with one small load on a short, drain-only cycle. Stand near the floor drain and watch for when the water flows into it and whether it backs up. This confirms whether the washer load specifically triggers the overflow.

2. Remove the floor drain grate and clear visible lint

Take the grate off and remove any lint, hair or soap scum you can see near the top of the drain. Use gloves and a flashlight. A hand tool or long plastic grabber works well for pulling out clumps without pushing them deeper.

3. Check the washer standpipe height and hose connection for kinks

Make sure the washer discharge hose is secured to the standpipe and not kinked or pushed too far down. The top of the hose should be inside the standpipe but not sealed tightly—leave an air gap if your machine instruction calls for it.
Confirm the standpipe is tall enough (typical residential height is 18–30 inches from the trap) so the washer can drain properly without creating a siphon or splashing.

4. Open the nearest cleanout and run a garden hose to test downstream flow

Locate the nearest cleanout (a capped fitting usually at floor level or outside near the foundation). Remove the cap carefully. Run a garden hose into the cleanout for a minute or two and watch the floor drain. If water backs up from the drain when the hose runs, there’s a downstream blockage. If water runs freely out the cleanout, the problem is likely near the standpipe or drain entrance.

5. Use a wet/dry vacuum at the drain to pull out lint and soap

With the grate removed, seal the vacuum hose over the drain as best you can and run the vacuum on high for 30–60 seconds. This often pulls out soft clogs of lint and soap. Empty the vacuum and repeat if you get material out, then re-test with a short wash.

6. Note whether only the washer load causes overflow

After cleaning and testing, run small tests of other fixtures (sink, tub) individually. If only the washer causes overflow, you can focus on the standpipe, hose, and lint. If multiple fixtures overflow at once, the blockage is farther down the line and you should consider professional help.

What Not to Do

Avoid pouring bleach or caustic drain cleaners down a lint-clogged standpipe. These chemicals can damage pipes, harm you through fumes, and are often ineffective against soft lint clogs.
Do not disconnect washer hoses while the machine is running or while the system is under pressure. That can spray water and cause injury or a bigger mess.
If multiple fixtures back up or you smell sewage, do not keep trying home fixes—stop and call a professional.

When to Call a Professional

Call a plumber if any of the following apply:

Opening the cleanout shows persistent backup or you can’t clear the blockage with a vacuum or hand tools.
Multiple drains and fixtures back up at once or you notice a strong sewage smell—this suggests a main-line issue.
You’re uncomfortable removing the cleanout cap or using service tools. A pro can safely inspect with a camera and clear deep clogs.

If your tests show backups only during the washer cycle but you can’t clear lint or the issue returns quickly, consider scheduling a service call. Also see guidance on overflow when multiple appliances run and overflow when appliances run together for related cases where more than one device affects drain capacity.

Safety Notes

Wear gloves and eye protection when reaching into drains.
Turn the washer off and unplug it before adjusting hoses or working near electrical connections.
Be careful when removing cleanout caps—sudden water release can occur. Stand to the side when loosening the cap and have a bucket or towels ready.
Avoid using harsh chemicals in areas where sewage exposure is possible. If you smell sewage, ventilate the area and call a professional.

Common Homeowner Questions

Why does only my washer cause the overflow? A: Washer discharge contains lint and soap that often clog the standpipe or nearby drain; other fixtures use less lint or empty more slowly.
Can I use an enzyme drain cleaner to fix this? A: Enzyme cleaners are safer than caustic chemicals and may help soften organic buildup, but they’re not a guaranteed fix for lint clogs. Mechanical removal is usually faster and more reliable.
How long should I try DIY fixes before calling a plumber? A: If simple cleaning, vacuuming, and the cleanout hose test don’t restore normal flow within an hour, or if multiple fixtures are affected, call a professional.