Drains smell because they’re alive. Well, biologically alive. Bacteria, mold, and biofilm (a slimy city of microbes) throw a non-stop party in your pipes.
They feast on soap scum, hair, and food scraps. Their waste? That sulfurous, rotten-egg gas you hate. It’s basically microbe flatulence. Charming, right?
You also get clogs. Stagnant water turns into a bacterial spa. It smells like a teenager’s gym bag left in the sun for a week.
