The answer to 'what causes drain trap' is a drain trap is a curved section of pipe installed under a sink, tub, or floor drain. Its purpose is to create a water seal that prevents sewer gases from entering the home. The curved shape of the trap holds a small amount of water, creating a barrier that blocks odors and pests from coming up through the drain.
Drain traps can become clogged or dried out over time, which can allow sewer gases to escape into the home. Common causes of drain trap issues include debris buildup, evaporation of the water seal, and improper installation or maintenance.