There was a week where our bathroom smelled faintly of rotten eggs every morning. I cleaned the toilet. I scrubbed the shower. I washed the bath mat. The smell stayed. It was coming from the sink drain.

Drain smells are not the drain itself rotting. It is bacteria feeding on the gunk coating the inside of your pipes. Hair, soap scum, skin cells, toothpaste residue — it all builds up into a biofilm that bacteria love.

The Instant Fix

Pour half a cup of baking soda down the drain. Follow it immediately with half a cup of white vinegar. Cover the drain opening with a wet cloth. You will hear fizzing — that is the reaction breaking up the biofilm. Let it sit 15 minutes. Then flush with a full kettle of boiling water. The heat kills remaining bacteria. This costs about fifteen cents.

For Stubborn Smells

If the baking soda and vinegar does not work, buy a bacterial drain cleaner (not a chemical one). These contain live bacteria that eat the biofilm. Pour it in at night when nobody will use the sink for 8 hours.

Prevention

Once a week, pour a kettle of boiling water down every drain. Just boiling water. This melts soap scum and grease before it builds up. Ten seconds of prevention saves the 15-minute deep clean. Also run the bathroom fan during and after showers — humidity feeds mold in every crevice.

The rotten egg smell in our bathroom? Gone in 20 minutes. My wife assumed I had called a plumber. She was not wrong to assume — I had been talking about it for a week without doing anything about it.