Does every plumbing fixture need a trap in Ontario?
Every fixture must be protected by a trap that provides a liquid seal between the drainage system and the room, and every trap seal must be protected by venting so it cannot be siphoned dry.
The trap's water seal is the only thing separating living space from sewer gas, which is why the code pairs every trap rule with a venting rule: without adequate venting, discharging fixtures create pressure swings that siphon or blow out trap seals. The code prescribes minimum seal depths, limits the fall between a fixture outlet and its trap, restricts double-trapping, and prohibits self-siphoning trap forms such as the S-trap — the classic defect found in DIY basement bathrooms, where a gurgling drain is the audible symptom of a trap being siphoned. Floor drains that rarely receive water need trap seal primers or deep-seal traps so the seal does not simply evaporate.
The U-bend under every sink holds a plug of water that blocks sewer gas from entering your home. Venting is what keeps that plug in place when water rushes through the pipes. A gurgling drain means the system is sucking its own seals dry — a venting defect, not a quirk.
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This page is provided for general information. Building code requirements depend on your specific project, occupancy and municipality, and code editions change. Always verify requirements against the current Ontario Building Code and confirm with your local building department.