So what about the glass and paper trick? This method may slightly reduce airflow into the drain, but only if it creates a tight seal. In most cases, an upside-down glass simply sits in the sink and does not seal the opening properly. The paper quickly absorbs moisture, loses its shape, and cannot provide reliable protection. Even a small movement or draft can shift the whole setup out of place.
A much better option before leaving is to do a few simple things. First, run water in every sink, shower, and bathtub for 10–20 seconds. This refreshes the water in the traps. Do not forget about floor drains, laundry rooms, and rarely used bathrooms. Toilets should also be flushed once.
If you will be away for a long time, it is better to close drains properly: with a standard stopper, a rubber plug, a silicone cover, or tightly applied plastic film or painter’s tape. The main goal is to reduce evaporation and create a physical barrier. For a very long absence, you can add a small amount of mineral oil to the drain. It creates a thin layer above the water and slows evaporation. It is important not to use cooking oil, because it can spoil and make the pipes dirty.
So, covering a sink with paper and a glass is not the best solution. Real protection comes not from the “hack” itself, but from a water-filled trap and a tightly closed drain. Before going on vacation, it is enough to flush all drains, cover them with reliable stoppers, and remove sources of bad odors, such as trash. This is simpler, cleaner, and much more effective.