To clean smelly drains effectively, start with these common and proven methods:

• Pour hot water or near-boiling white vinegar slowly down the drain to help soften and wash away buildup causing odor.
• Use a baking soda and vinegar mixture: pour about ½ cup baking soda followed by 1 cup vinegar into the drain. Let it fizz and sit for 30 minutes to an hour, then flush with hot water. This combination neutralizes smells and cleans debris clinging to pipes.
• Clean the P-trap by removing it under the sink, emptying and rinsing out any trapped gunk that causes odors, then reassembling.
• For kitchen sinks with garbage disposals, run hot water and turn on the disposal to clear food scraps. Freshen with citrus peels by grinding them in the disposal.
• If odors persist, consider using a professional drain cleaner product safe for your pipes, like Drano Max Gel, which cuts through buildup and odors.

Additional tips:

• Avoid excessive use of bleach as it can damage pipes, but diluted bleach can sanitize drains when used cautiously.
• Regular maintenance with monthly baking soda and vinegar treatments can keep drains smelling fresh.
• Make sure water stays in the P-trap to block sewer gases; refill the trap with water if necessary.

These methods work for bathroom, kitchen, and laundry drains with foul odors caused by gunk, food waste, or sewer gas.