A viral travel hack suggests covering a sink drain with paper and an upside-down glass before leaving home to stop sewer odors and insects.While the idea is based on a real plumbing principle, experts say the method is unreliable.

The key is the P-trap, the U-shaped pipe under drains that holds water to create a “water seal” blocking sewer gases and pests.If a drain goes unused for weeks, the water can evaporate, especially in hot or dry conditions, allowing odors or insects inside.

Although covering the drain may seem helpful, “Unless the upside-down glass creates a tight seal over the drain opening, it’s unlikely to do much of anything.”The paper can also become damp and fail to seal the drain.

Instead, before a long trip, run water through every sink, shower, and tub to refill the P-traps, then seal drains with existing stoppers, rubber plugs, silicone drain covers, or plastic wrap.For extended vacations, adding a tablespoon of mineral oil can slow evaporation.