That’s a traditional household tip that’s common in some places. The idea is to block odors and discourage insects from coming up through the drain while the house is unoccupied.
Here’s how it’s supposed to work:
- The paper acts as a simple barrier over the drain opening.
- The upside-down glass holds the paper in place and creates a more effective seal, reducing airflow from the drain.
In practice, it may help a little, but there are more reliable ways to prepare your drains before leaving:
- Run water in every sink, shower, and floor drain just before you leave. This fills the drain’s P-trap with water, which is the main barrier that prevents sewer gases and many insects from entering the home.
- If you’ll be away for several weeks or longer, adding a small amount of mineral oil (about 1–2 tablespoons) to infrequently used drains can slow the water in the P-trap from evaporating.
- Make sure the sink is clean and free of food residue so it doesn’t attract pests.
- If you’re only away for a few days or a couple of weeks, simply filling the P-traps with fresh water is usually sufficient.
So, covering the drain with paper and an upside-down glass isn’t harmful and may provide an extra barrier, but it’s generally not necessary if your plumbing is functioning properly and the drain traps contain water. The most important step is ensuring the P-traps are full before you leave.
