Quick Answer:
Intermittent backups in more than one drain usually mean a partial blockage or an intermittent pump/ejector problem. Start by tracking exactly when backups happen and what fixtures are running. Inspect any sewer ejector or pump basin for abnormal cycling and float-switch behavior, and during an active event briefly check the main cleanout for a pressure buildup or release. If the problem is unpredictable, arrange a timed camera inspection to find roots, grease, or collapsed pipe sections. For related rapid-onset events see Multiple drains clog suddenly and for backups tied to utility outages see Multiple fixtures back up after city outage.
Why This Happens
- Partial blockages: roots, grease, or debris can narrow the main sewer so flow is restricted and only causes trouble when multiple fixtures run or the flow rate rises.
- Pump/ejector issues: a damaged or sticky float switch, failing pump, or clogged basin can cause intermittent cycling or a temporary loss of discharge capacity.
- Pressure behavior: trapped air or a valve problem can let pressure build until it suddenly releases, producing sporadic backups.
- External events: heavy rain or municipal issues can overload the system at times, making the problem come and go.
Step-by-Step What to Do
1. Log times and activities
Keep a simple log for several days. Note the exact time of each backup and what was running nearby (dishwasher, laundry, shower, heavy rain). Look for patterns, for example:
- Backups during laundry/dishwasher cycles
- Only after heavy rain
- Nighttime cycling when no fixtures are used
2. Observe the ejector/pump basin
Locate your building sewer ejector or pump basin and watch it from the outside while someone runs a fixture. Look for:
- Frequent short cycles (pump coming on and off rapidly)
- Very long runs or no runs at all when wastewater enters the basin
- Humming, grinding, or unusual noises from the pump
- Float switch sticking or failing to move freely
If you need to open the basin lid, turn off power at the breaker first and take care to avoid contact with sewage. If you are not comfortable doing this, stop and call a plumber.
3. Briefly test the main cleanout during an event
When a backup is actively happening, the main cleanout can tell you if pressure builds and then releases (a sign of partial blockage). From a safe distance:
- Visually inspect the cleanout cap for bulging, puddling, or surges.
- If you are experienced and properly protected, you can cautiously loosen the cap a small amount to see if pressure vents — do not fully remove the cap or expose yourself to spray. If unsure, skip this and call a pro.
4. If it’s intermittent and unpredictable, schedule a timed camera inspection
An unpredictable issue is often caused by roots, grease buildup, foreign objects, or a structural problem that only shows under certain flows. Ask a plumber for a timed camera run: they will watch the sewer camera while you run laundry/dishwasher or wait for a natural event so they can see what happens in real time.
What Not to Do
- Avoid repeatedly snaking the line for intermittent issues without camera confirmation — this can mask underlying damage and may push debris farther into the pipe.
- Do not ignore abnormal pump cycling or unexplained sewage odors — these often indicate a failing component or growing blockage.
- Don’t remove pump-basin or ejector lids without switching power off and without appropriate protective equipment.
- Call a professional when backups are unpredictable, pumps cycle abnormally, or a camera inspection is recommended rather than attempting repeated DIY fixes.
When to Call a Professional
- Backups are unpredictable or getting worse despite your checks.
- Your ejector/pump cycles rapidly, runs constantly, or makes unusual noises.
- Visible sewage or strong sewage smell in the home.
- You need a timed camera inspection to locate roots, grease, or collapsed sections.
Safety Notes
- Sewage contains pathogens — wear gloves, eye protection, and work clothes you can wash or discard.
- Avoid standing in or near pooled sewage; keep children and pets away.
- Turn power off at the breaker before opening pump or ejector covers. If you are unsure about electrical or confined-space risks, wait for a professional.
- Do not mix chemical drain cleaners with other cleaners or use them in pump basins — they can damage equipment and create hazardous fumes.
Common Homeowner Questions
- Q: How long should I track backups before calling a plumber?
A: Log events for a few days to a week; call sooner if backups are frequent, produce sewage, or involve the pump basin. - Q: Can I run the washer while waiting for a plumber?
A: Avoid running major fixtures together if backups have recently occurred; run small tests only if it helps capture the issue for a timed camera inspection. - Q: Will a camera inspection damage my pipes?
A: No — a camera is noninvasive and is the recommended way to diagnose intermittent or hidden main-line problems safely.
More in this topic
For more related fixes and similar symptoms, see Multiple Fixtures Backing Up Together.