Rotten-egg odour? Sewer gas is more than just a nasty smell. Hydrogen-sulfide (H₂S) can trigger headaches, nausea, and—in extreme concentrations—respiratory collapse. Learn the health risks of sewer-gas, the 9 most common causes (dry P-traps, failed wax rings, vent leaks, cast-iron cracks), and the DIY vs. plumber fixes that work under Ontario’s 2024 Plumbing Code. This guide shows you how to pinpoint odours quickly, apply safe DIY fixes, and know when to call Anta Plumbing for code-level repairs.
Top Causes of Sewer-Gas Odours (Ranked from Most to Least Common)
# | Source | Symptom Snapshot | Quick Test |
1 | Dry P-trap in little-used shower, floor drain, or laundry tub | Smell strongest at the fixture after vacations or winter | Shine a flashlight—no standing water? Add 2 cups water + 1 tbsp mineral oil to slow evaporation. |
2 | Failed toilet wax ring | Toilet rocks, water stain at base, constant odour | Gently push bowl—any wobble = replace ring & flange bolts. |
3 | Missing / undersized vent stack or clogged roof vent | Gurgling drains + odor after large flushes | Run water; listen for gurgle. Clear leaves/ice from vent; new 2024 OBC now allows air-admittance valves ≥ 100 mm above fixture. |
4 | Debris in sink overflow channel | Odour only at one basin | Flush overflow with 1:5 bleach solution or enzyme cleaner. |
5 | Hairline leaks in PVC or cast-iron behind walls/floor | Musty sewage smell + damp drywall | Call for smoke test or sewer camera. |
6 | Cracked cast-iron stack (pre-1970 homes) | Intermittent smell near stack chase | Video-scope; consider PVC replacement. |
7 | Siphoned trap from improperly sloped waste line | Odour follows use of nearby high-flow appliance | Check slope (2 % rule) and venting per code. |
8 | Clogged vent line (bird nest/ice cap) | Odor after storms; slow drains | Rod or hydro-jet to roof. |
9 | Foundation sewer leak | Odor in basement, damp slab | Hydrostatic test + camera → trench-less spot repair. |
Sewer smell in house – First-Response Safety & DIY Checks
- Ventilate fast: Open windows/doors; H₂S is heavier than air—place a fan low to the floor.
- Top up every P-trap: Pour 2 cups water in each floor/basin drain; add a splash of mineral oil to slow evaporation.thespruce.com
- Inspect toilet stability: If bowl rocks even slightly, shut off water, drain bowl, and plan a wax-ring swap before reuse.
- Roof-vent glance: From ground level, confirm the vent stack isn’t capped by snow, leaves, or a critter screen.
- When to exit & call 24 h emergency: If odour causes dizziness or the smell is strong in multiple rooms despite ventilation—hydrogen-sulfide can reach dangerous ppm quickly.
Step-by-Step Fixes for the Nine Odour Sources
|
# |
DIY / Pro Fix |
Supplies & Time |
When to Call a Plumber in Toronto |
|
1 · Dry P-Trap |
Re-prime with 2 cups water, then pour 1 Tbsp mineral oil so it floats on top and slows evaporation. |
Cup + mineral oil · 5 min |
Trap keeps drying every week → check house venting. diy.stackexchange.com |
|
2 · Failed Wax Ring |
Shut water; drain & unbolt bowl. Scrape old wax, set new no-squeeze wax ring + brass flange bolts; re-seat bowl square. |
Ring kit ≈ $9 · 45 min |
Flange rusted, floor soft, or bowl still rocks. |
|
3 · Blocked / Missing Vent |
From roof, clear leaves/ice with garden hose; for homes lacking a vent, add a 100 mm-min AAV above flood rim (2024 OBC-7.5.9.2). clearview.caleeds1000islands.ca |
Stack undersized, multiple gurgling fixtures → full code upgrade. |
|
|
4 · Sink Overflow Gunk |
Mix 1 : 5 bleach + hot water; squirt into overflow with turkey baster, wait 10 min, rinse. |
Bleach ≤ $1 · 15 min |
Odour back next day → debris in branch line. |
|
5 · Tiny Pipe Leaks |
Snap a photo of damp drywall; cut 6 × 6 cm peephole; sniff for H₂S. Patch if dry, call if wet. |
Drywall knife · 30 min |
Any moisture or sulphur smell = smoke test. |
|
6 · Cracked Cast-Iron Stack |
TEMP: Seal crack with epoxy putty sleeve. |
Putty $15 · 20 min |
Schedule stack-swap to PVC—epoxy buys weeks, not years. |
|
7 · Trap Siphon |
Verify branch slope (2 %); add AAV if vent tie-in impossible. |
Level & 50 mm ABS tee · 1 h |
Multi-story re-venting needed. |
|
8 · Clogged drain/ Vent Line |
Snake from roof or use garden hose on pulse; stubborn scale → hydro-jet. |
Hose · 30 min |
Hire pro hydro-jet rig for full 3-storey vent scrub. antaplumbing.com |
|
9 · Foundation Sewer Leak |
DIY pressure test rarely works—book camera + hydrostatic test. |
— |
Trench-less spot repair or CIPP liner. |
Safety first: If odour causes headache or dizziness, vacate and ventilate—H₂S becomes toxic above ~150 ppm.
2024–25 Ontario Code & Permit Essentials
- Air-Admittance Valves (AAVs) – Now legal as vent terminals if ≥ 100 mm above the fixture drain (OBC 7.5.9.2).
- Vent-terminal frost protection – Stack must enlarge one pipe size or be insulated where it penetrates the roof.
- Permit triggers – Any material change to a vent or waste line requires a Toronto plumbing permit; roof-only vent cleaning does not. toronto.ca
- AAV distance rule – Keep min. 200 mm above trap weir and accessible for inspection.
- Hydro-jetting & camera work – Classified as maintenance; no permit needed unless pipe replaced.
Tip: Pull Ontario One Call locates if you plan to break any walls or floors—hidden gas lines can share chases with vent stacks.
5 Pro-Level Diagnostics We Bring to Site
|
Tool |
What It Finds |
Typical Fee |
Turn-around |
|
Smoke Test |
Pin-holes & loose fittings behind walls/floors |
$350 flat |
2 hrs |
|
HD Camera Scope |
Cracks, roots, debris in stacks & laterals |
$275 (incl. USB video) |
90 min |
|
Hydro-Jet Vent Scrub |
Clears sludge, nests, grease (up to 200 ft) |
$3 – $5/ft |
Same-day |
|
Gas Detector (H₂S ppm) |
Confirms safe re-entry < 10 ppm |
Included |
30 min |
Hydro-jetting restores a factory-clean inner wall—gasses have nowhere to hide.antaplumbing.com
Sewer-Smell Gone in One Visit → Call Anta Plumbing Toronto
Call us for Toronto Drain cleaning services at ANTA Plumbing, we offer 24/7 emergency plumbing services and diagnostics for any drain issues
Why Anta? | Your Benefit |
Certified smoke-testing crew | Pin-points leaks without demo. |
Roof-safe hydro-jet rigs | Clears vent stack from the roof—no scaffolds. |
CIPP & spot-repair team | Fix cast-iron cracks same-day, trench-less. |
Up-front flat pricing | No Sunday/emergency surcharge. |
Spring 2025 promo: Free H₂S air-quality meter (value $85) with any odour-diagnosis call booked before 31 Aug 2025.
☎ 416-555-0123 📧 [email protected] 💬 WhatsApp 24-h
Frequently
Asked Questions
Yes—H₂S above 150 ppm can knock you out; prolonged low-level exposure causes headaches.omegaenv.com
Every 4–6 weeks or after each vacation; add mineral oil to slow evaporation.diy.stackexchange.com
No—minor fixture maintenance is exempt.
Yes, if located ≥ 100 mm above fixture and accessible, per 2024 OBC update.clearview.caleeds1000islands.ca
No—pressure is calibrated; camera inspection confirms pipe integrity first.antaplumbing.com
