Quick Answer:
Start by running cold water briefly in each fixture individually to flush standing water before heavy use. Check traps and the sewer cleanout for obvious problems. If sewage or a backup appears the first time you run water, stop using appliances and call a professional to camera the line—this can indicate roots or long-term buildup.
Why This Happens
When a house sits unused, water in drains can evaporate and P-traps can go dry, letting sewer gas through. Small amounts of standing water also let biofilms form and bad smells develop. In some cases debris, rodent entry, tree roots or long-term buildup in the main sewer collect while you’re away and only show themselves when you start using water again.
Step-by-Step What to Do
1. Flush each fixture briefly
- Go to every sink, shower, tub and outside spigot. Run cold water briefly in each fixture individually to flush standing water before heavy use. A short flow clears stale water without overwhelming drains.
2. Check and refill traps
- Smell or gurgling from a single fixture often means a dry trap. Pour a small amount of water into seldom-used drains (floor drains, guest baths, basement showers) to refill the trap and reseal the drain from sewer gas.
3. Inspect the sewer cleanout
- Locate the sewer cleanout (usually a capped pipe near the foundation or in the yard). Look for loose caps, debris, or signs of rodent entry. If you see obstruction or sewage at the cleanout, don’t run multiple fixtures—this points to a main-line problem.
4. If a backup happens on first use
- If water or sewage backs up the first time you use a fixture after a long absence, stop. Avoid running appliances (dishwasher, washing machine, sump pump) that could push more sewage into the house.
- Call a licensed plumber to camera the line for root intrusion or long-term buildup rather than trying aggressive fixes that may worsen the issue.
5. Preventive follow-up
- After flushing and refilling traps, run a modest amount of water through floor drains and seldom-used fixtures once a week while you’re away in the future. For related situations, see Basement drain floods randomly and check the cluster hub topic Basement Floor Drain Backups for broader guidance.
What Not to Do
- Don’t assume old water odor equals a major break—avoid using powerful chemical treatments blindly. Heavy chemicals can damage pipes, septic systems or make the problem worse.
- Don’t run washers, dishwashers or pumps if you see any sewage or persistent backup on first use. Call a pro when backups happen immediately on first use after vacation, when sewage appears, or when multiple fixtures show obstruction.
When to Call a Professional
- Call a plumber if you see sewage, if multiple fixtures are obstructed, if the sewer cleanout shows debris or rodent damage, or if a backup happens immediately on first use after vacation.
- Ask the pro to camera the line when you suspect roots or long-term buildup—video inspection finds blockages and avoids unnecessary excavation.
Safety Notes
- Avoid contact with standing sewage. Wear gloves and eye protection and wash hands thoroughly afterward.
- Do not mix chemical cleaners. Strong chemicals can create dangerous fumes or react with one another.
- If a basement or electrical area is flooded, shut off power to that area before entering and contact an electrician or plumber if you’re unsure.
Common Homeowner Questions
- Why do drains smell after vacation? — Traps may have dried out and allowed sewer gas through; refilling the trap usually fixes it.
- Can I use enzyme cleaners to clear buildup? — Enzyme cleaners are safer than harsh chemicals for routine maintenance, but don’t rely on them for major backups; a camera inspection is better for diagnosing serious buildup.
- What does it mean if several fixtures back up at once? — That often means a blockage in the main sewer line; stop using water and call a professional to inspect the line.
Related Articles
If you’re seeing a related symptom, these may help:
- Backup after long vacation
- Basement drain floods randomly