Summer holidays are meant to smell like sunscreen and pine forests, not like an old plughole. Yet closed windows, high temperatures and dry plumbing pipework can quietly turn your empty flat or house into a small gas chamber of drain odours. A simple, almost ridiculous trick with a glass and a paper towel can stop that from happening before you lock the door.
Why your sink turns on you when you’re away
Every sink in your home has a hidden bodyguard: the U-shaped or P-shaped bend in the pipe under the basin. That bend holds a pocket of water called a “trap seal”.
That tiny water barrier works like a plug for gas. It blocks smelly air from the main drain line and sewer, while still letting wastewater flow through.
A few centimetres of water in the trap are the only thing separating your living room from raw sewer gas.
When you use the sink regularly, fresh water keeps topping up the trap. In summer, especially in a hot, dry room, that water slowly evaporates. When you disappear on holiday, nothing refills it.
As the trap dries out, the seal shrinks. Once it drops low enough, gases in the pipe get a clear path into your home. Those gases carry sulphur compounds and other volatile chemicals that smell like rotten eggs, damp laundry and old food waste.
Some older buildings come with a bonus: dry traps can allow tiny pests such as drain flies or cockroaches to creep up through the system. You only notice them when you’re unpacking your flip-flops.
The oddly clever glass-and-paper towel trick
Here is where the glass and paper towel routine earns its place in every holiday checklist. It looks silly, but it is rooted in basic physics.
How to set it up in under a minute
- Run the tap for 10–15 seconds to make sure the trap is fully topped up.
- Take a sheet of kitchen paper and dampen it under the tap, then wring it out so it is moist, not dripping.
- Lay the damp paper flat across the plughole or strainer in the sink.
- Place a drinking glass or mug upside down over the centre of the drain, trapping the paper beneath it.
- Repeat for every sink you won’t touch while you’re away: kitchen, bathroom, utility room.
The glass creates a bubble of still, humid air above the drain, and that slows evaporation from the trap dramatically.
➡️ Heavy snow confirmed to intensify tonight as visibility could collapse in minutes
➡️ Place this object near your orchid : blooming starts in just a few days
➡️ Auto technicians explain how keeping the gas tank above half prevents fuel line freeze
➡️ Psychology says people who sleep in the same bed as their pets often have these 10 quiet strengths
Why this low-tech shield works
Evaporation speeds up when air can move freely across a wet surface and carry water vapour away. In a typical kitchen, air from open windows, fans or even convection currents does exactly that.
By covering the drain with a damp paper towel and an inverted glass, you change those conditions.
- The glass blocks air movement directly over the plughole.
- The damp paper helps seal tiny gaps and raises humidity in that small space.
- The trapped pocket of air becomes saturated with moisture, so the water below evaporates far more slowly.
The result: the trap holds onto its water for much longer, often long enough to survive a two–four week summer break without drying out.
What about toilets, showers and floor drains?
Your sink is only one part of the story. Any fixture connected to your drainage system relies on a water seal.
| Fixture | Quick holiday prep | What it achieves |
|---|---|---|
| Kitchen sink | Top up trap, cover with damp paper and inverted glass | Reduces evaporation and blocks airflow into the drain |
| Bathroom sink | Same glass-and-paper method as the kitchen | Keeps trap sealed in hot, closed bathrooms |
| Shower or bath | Run water, cover the drain with cling film and weigh it down with a bowl or pan | Makes a simple vapour cap over wide grates |
| Floor drain | Add water, then a teaspoon of mineral oil, cover with a plate | Oil floats on top and slows evaporation; plate cuts drafts |
| Toilet | Leave water in the bowl, close lid and seat | Limits air movement over the bowl’s water seal |
Showers and baths often have larger drains that are harder to cap with a glass. A stretch of plastic film pressed flat over the grate, with a heavy bowl or pan on top, works in a very similar way to the glass trick.
Toilets already have a built-in water seal in the bowl. Just avoid shutting off the water supply unless you really need to, and keep the lid down to reduce air movement.
Extra layers of protection for long trips
If you are leaving your home empty for three weeks or more, or you live in a particularly hot city flat, you can go a little further.
- After topping up each trap, add a teaspoon of food-grade mineral oil to the drain. The oil floats on the surface and forms a thin barrier against evaporation.
- Clear the sink of food debris, coffee grounds and grease so there is nothing rotting in the strainer while you are away.
- Before the trip, freshen the waste arm with half a cup of baking soda, followed by half a cup of warm white vinegar, then flush with hot water after a few minutes.
- Pour a cup of water into rarely used drains like laundry standpipes or garage floor drains.
- Set your thermostat to a moderate temperature rather than letting the property bake. Cooler rooms slow evaporation.
Think of each drain as a tiny reservoir: keep it full, keep it covered, and it quietly guards your indoor air the whole time you are gone.
Back from holiday and greeted by a smell? Here is a recovery plan
If you are reading this a bit late, with the windows already open and your nose wrinkling, you can still reset things quickly.
- Open windows and, if possible, doors for short bursts to flush stale air out.
- Run cold water at every sink for 30–60 seconds to refill the traps.
- Flush toilets and run the shower for 15–20 seconds.
- Use the baking soda and vinegar routine on smelly sink drains, chasing it with hot water.
- If one particular sink still reeks, remove the U-shaped pipe (the P-trap), rinse it in a bucket outside, and reinstall it with fresh washers if it leaks.
Most musty drain smells fade within an hour or two once fresh water has restored the seals. Persistent odours can point to other issues such as cracked pipework, poorly vented systems or a hidden leak, which may need a professional plumber.
What science says about your summer drains
Standard traps in homes usually hold around 50 millimetres of water, roughly two inches. In volume terms, that is only a cup or less, yet it is more than enough to block rising gases when the seal is intact.
The rate at which that water disappears depends on a few factors:
- room temperature
- humidity level
- airflow around the drain
- length of time the fixture sits unused
In a shaded, cool bathroom with the door closed, a trap might stay wet for a month. In a sunlit kitchen with the window cracked and a fan on low, the same trap could dry in a week. There is no precise timetable, which is why simple prevention tricks are valuable.
Beyond smell, those rising gases often contain low levels of hydrogen sulphide and ammonia. For most people, exposure at household levels is just unpleasant. For those with asthma, migraines or sensitive sinuses, it can trigger headaches or nausea.
Small risks, smart tweaks and what to avoid
Using a little oil on drains is broadly safe when done sparingly. Mineral oil is ideal because it does not go rancid. Vegetable oils can oxidise and become sticky, which may leave residue in cold pipes if used often.
If your home drains into a septic tank, tiny amounts of oil now and then will not wreck the bacterial balance, but pouring generous glugs down every month certainly will not help. Stick to teaspoons, not tablespoons, and only before long absences.
Be cautious mixing homemade cleaners with leftover chemical drain openers. If you recently used a harsh caustic product, leave the line alone rather than adding vinegar, which can cause fizzing or spluttering in the pipe.
There is also the practical side: if you share your home with cats, dogs or small children, pick a heavy mug or tumbler for the sink covers. Lightweight glasses tipped by a curious paw defeat the whole point.
Turning the trick into a real-life checklist
The neat thing about the glass and paper towel move is how fast it is. A typical flat with a kitchen sink, a bathroom sink and a shower can be prepped in under five minutes.
- For a weekend away: run each tap briefly and use the glass trick on sinks. That is usually plenty.
- For a week or two in peak heat: add covers to shower and floor drains, and consider a teaspoon of mineral oil in the least-used drains.
- For a month-long trip: do the full works – water top-up, small oil layer, glass or plastic covers, toilet lids down, and thermostat set lower.
If you prefer numbers, think of a trap holding roughly 200–300 millilitres of water. In hot, dry conditions, evaporation might nibble away 5–10 millilitres a day. Left fully exposed, your seal could drop too low in two to four weeks. Restrict airflow with the glass-and-paper cap, cut room temperature, and you stretch that timeline comfortably beyond most holidays.
One damp paper towel, one upside-down glass, and you walk back into a home that smells like your home, not the local sewer line.