Why does my bathroom drain smell bad?

Bad bathroom drain smells are typically caused by dried-out P-traps, buildup of hair and soap scum, or sewer gas escaping through compromised seals. The most common culprit is a dry P-trap - the curved section of pipe under your drain that should always hold water to block sewer gases.

If a bathroom isn't used regularly, the water in the P-trap can evaporate, allowing sewer gases to rise up through the drain. This is especially common in guest bathrooms, basement bathrooms, or floor drains. The solution is simple: run water for 30 seconds to refill the trap. For drains that aren't used often, pour a small amount of mineral oil down the drain after running water - it floats on top and slows evaporation.

Buildup in the drain is another frequent cause. Hair, soap residue, and bacteria create a slimy biofilm that produces unpleasant odors. You can often resolve this by removing the drain cover and pulling out visible hair and debris, then flushing with hot water. For deeper cleaning, pour half a cup of baking soda down the drain, followed by white vinegar, let it sit for 15 minutes, then flush with hot water.

In Ottawa's older homes, damaged or improperly installed plumbing can also cause persistent odors. If the smell continues after trying these solutions, or if you notice gurgling sounds or slow drainage, there may be issues with the vent stack, damaged seals, or improper trap installation that require professional attention.

When to call a professional: If odors persist after cleaning and ensuring P-traps are filled, or if you smell sewer gas throughout the bathroom rather than just at the drain, contact a licensed plumber. These symptoms can indicate serious plumbing issues that need immediate attention to prevent health hazards and potential damage.