Pour 1 cup of white vinegar into the drain to kill smelly mold spores. Allow the vinegar to sit in the drain alone for 10 minutes.
Add 1/2 cup baking soda and 1/2 cup table salt to the drain to loosen soap scum, grease and residue inside the drain. Allow the baking soda and vinegar to foam and remain inside the drain for 10 minutes.
Rinse the drain with water for one minute to wash away the baking soda, salt and vinegar, as well as the loosened gunk inside the drain.
Pour 1/4 cup of lemon juice down the drain each week to maintain its freshness. Leave the lemon juice in the drain for 30 minutes before rinsing it away.