A bad smell from a drain is most often caused by a failed or dry water seal in a trap, allowing sewer gases to escape into the room. Other common sources include accumulated organic matter inside the waste pipe, a cracked soil stack, a blocked vent or a defect in the underground drain. In older North London properties with cast iron stacks, internal corrosion can create pinhole leaks that release odour at high level. Building Regulations Part H1 requires every waste fitting to be served by a trap with a minimum water seal depth, typically 50mm or 75mm depending on application. Engineers usually address common causes by topping up dry traps, replacing failed seals and clearing organic residue from waste pipes. A CCTV inspection helps locate hidden defects on the underground section.
Bad smell from drain
Unpleasant odour rising from a drain or fitting, usually indicating a trap or seal problem.
