Bathrooms or floor drains that rarely get used—like in guest rooms or store areas—tend to dry out. The water trap inside them (the U-shaped bit) is meant to hold a small amount of water that blocks sewer gases from coming back up. When it dries, smells can drift through the drain and into the room.
Pouring a bucket of clean water down these drains occasionally keeps the trap filled. You maintain that water “seal” and prevent bad odours from sneaking in. It also washes away any early buildup of soap scum or hair before it becomes a blockage.
It’s a five-minute job that keeps infrequently used spaces from developing that stale, forgotten-bathroom smell.