Drain or manhole cover smelling outside the house
Check the steps below first — if you're not confident, get it fixed safely today.
Post a job — we'll find you an engineer →⚠️ Never enter a manhole chamber without proper confined space training and equipment. Sewer gas (methane, hydrogen sulphide) can be lethal. Only look from ground level.
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Most likely cause & what to check
A sewage smell from outside drains is usually caused by a blockage in the underground drainage system causing waste to back up and gas to escape, a cracked or broken drain allowing effluent to seep into surrounding soil, or a dry trap in a rarely used gully (a floor-level drain grille).
Locate your manholes — lift the cover using a flat-bladed tool (they are heavy: use two hands and stand to one side). Look inside from above at ground level. If the chamber is full of sewage, there is a blockage downstream (between this chamber and the next one, or between it and the sewer connection).
Check all gullies (the ground-level drain grilles around the property) — these are where downpipes, kitchen waste, and yard drainage connect to the system. Each has a water seal in the trap below. If a gully has not been used recently, the water seal may have evaporated, allowing sewer gas up. Pour a bucket of water down each gully to refresh the seal.
If a chamber is dry (no water in it) but smelling, the vent pipe may be blocked or missing — sewer gases are venting back through the property rather than up the vent stack.
If chambers are backed up: try clearing with drain rods (available to hire, or a drainage company can jet the drain). Rod from the highest chamber downstream — push rods in, attaching additional sections, and rotate clockwise only (anti-clockwise unscrews rods and they can be lost in the drain).
If you cannot clear the blockage with rods, or if the drain appears cracked or collapsed, a drainage engineer with CCTV survey equipment is needed. Many councils and water companies offer free drain surveys for blockages that affect their main sewer.
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Frequently asked questions
Why does my drain smell worse in warm weather?
Warm temperatures accelerate bacterial decomposition of organic matter in drains and sewers, producing hydrogen sulphide and other gases. A drain that barely smells in winter can be quite unpleasant in summer. This is especially noticeable from inspection chambers and gullies that trap decomposing material.
Can a drain smell indicate a blocked or damaged sewer?
Yes — a persistent outdoor drain smell that worsens over time, especially if accompanied by slow drainage from indoor fixtures, may indicate a collapsed or cracked drain pipe that is allowing sewer gas to escape. A CCTV drain survey (£100–£300) can identify the exact location and nature of any damage.
Who is responsible for smelly drains near my property?
Drains within your property boundary that serve only your property are your responsibility. The main sewer in the street is your water company's responsibility. If your inspection chamber is clear but the smell comes from beyond your boundary, contact your water company — they are obligated to address public sewer issues free of charge.