The simple glass and paper trick to stop drains stinking after a sunny spell away

That unpleasant whiff can start building up while your home is shut up and quiet.

As temperatures rise, heat accumulates and the air inside dries out. With no daily use, your plumbing effectively goes on pause too. When that happens, the parts designed to block odours can stop doing their job. One quick, simple hack can slow it all down while you’re off enjoying the sunshine.

Why drains stink after a sunny spell away

The reason your sink usually doesn’t smell is the water seal held in the U‑bend. That curved section keeps a small reservoir of water in place, which blocks sewer gases from drifting back into the kitchen. During hot weather, that water can evaporate surprisingly quickly. Once the bend dries out, air from the waste pipe can pass straight through, bringing a sour, sulphurous smell along with it.

There’s another contributor too: biofilm lining the inside of pipes can give off gases when it’s left sitting without disturbance. With the windows shut, those odours collect indoors until the moment you come back and open the door.

Bathrooms are affected in exactly the same way. Showers, baths and even floor drains rely on similar traps. A long summer trip can be just the right length of time for a U‑bend to dry out. The best time to deal with it is before you set off.

“Keep the U‑bend wet and you keep the stink out. Protect the water seal, and the house greets you with clean air.”

The glass and paper trick, step by step

This simple, no‑frills cover reduces evaporation from the trap. It’s very cheap and takes about a minute to do.

• Let the tap run for 10–15 seconds to top up the U‑bend.
• Place a sheet of damp kitchen paper over the plug‑hole.
• Turn a clean glass or mug upside down and set it over the paper so it covers the hole.
• Sit it firmly against the sink to reduce airflow around the waste.
• Do the same for utility sinks, baths and showers, using a larger cup or bowl where needed.

Why it helps: evaporation happens faster when it’s warm and when air is moving. The glass acts as a barrier to airflow at the plug‑hole, while the damp paper supplies moisture and closes small gaps. Together they create a still, humid pocket above the trap water, helping the U‑bend stay wet for much longer.

“A damp sheet plus an upturned glass makes a near‑airtight cap, which slows water loss from the trap for weeks.”

When a plug works even better

If you already have a snug rubber plug, that’s often the best option. Before fitting it, add an inch of water to the bowl. That extra layer helps seal the waste and adds a bit of weight.

A basket strainer with a tight seal can work similarly. In a shower, a silicone drain cover gives a tidy seal without needing tape.

Other quick moves before you lock the door

You can combine a few basic steps to make drain odours even less likely.

• Tip a teaspoon of vegetable oil into each drain to create a thin layer on top of the trap water.
• Flush the loo, then stretch cling film tightly over the bowl to reduce evaporation. Take it off when you’re back.
• Wash the sink strainer and throw away any food scraps to avoid nearby smells.
• Add half a cup of bicarbonate of soda to the sink, followed by a cup of warm white vinegar. Once the fizzing stops, rinse through with hot water.
• Pour a cup of water into floor drains that aren’t used often. Add a few drops of oil there too.
• Leave dishwasher and washing machine doors slightly open to stop stale, musty odours building up inside.

The eco and cost angle

These methods can reduce reliance on strong deodorisers. They mainly use things most households already have. They can also help you avoid a call‑out if a dried trap starts producing smells.

Method	Where to use	Upfront cost	Time	Notes
Glass + paper cap	Kitchen, utility, bath, shower	£0–£1	1 min	Best quick fix for airflow control
Plug and shallow water	Sinks with a tight plug	£0	1 min	Strong seal, check for slow leaks
Vegetable oil film	Any trapped drain	Pennies	30 sec	Slows evaporation on hot days
Bicarb + vinegar rinse	Sinks and showers	£0–£2	10 min	Loosens organic build‑up before you go
Cling film on loo	Toilet bowl	£0–£1	1 min	Keep pets and kids away
Neighbour trap top‑up	Whole house	Tea and thanks	2–3 mins	Great for trips over two weeks

How long a water seal actually lasts

In hot, dry weather, a small trap can dry out within a week. A deeper bath trap can hold on longer, but airflow can still speed up the loss. By cutting down air movement, the glass cap slows evaporation.

In many houses, that can extend the safe window to several weeks. Humidity plays a part as well: a cooler, shaded kitchen typically loses less water than a loft bathroom that gets full sun.

Risks to watch and what to avoid

• Don’t leave bleach sitting in the trap, as it can harm metal components and seals.
• Skip metal cups that might rust; glass, ceramic or plastic are better for the cap.
• Make sure the area is clear so the glass can’t be knocked over before you go.
• For longer trips, turn off the mains stopcock to reduce the risk of leaks elsewhere.
• If you use a septic tank, keep vinegar use reasonable and steer clear of heavy chemical cleaners.
• In hard‑water areas, limescale can build up; a quick descale before leaving keeps outlets looking tidy.

Bathrooms and little‑used drains need the same care

Showers are often the first to smell because hair traps and soap scum provide food for bacteria. Rinse the trap through with hot water, then use either a silicone cover or the glass‑and‑paper cap.

For baths, close the pop‑up waste and leave a shallow layer of water above it. Utility floor drains can dry out without you noticing, so top them up and add a few drops of oil to help maintain the seal.

Appliances and hidden odours

Dishwashers and washing machines also tie into the waste line. If a filter has gone stale, the whole run can start to smell. Clean the filters, empty any standing water, and leave the doors ajar.

In the week you travel, run an empty hot cycle with soda crystals. Your waste hose will be better off for it later.

A simple pre‑holiday checklist you can keep

• Top up U‑bends by running water for 10–15 seconds.
• Add the glass‑and‑paper cap to sinks and showers.
• Seal baths and leave a shallow layer of water.
• Put a teaspoon of vegetable oil into each trap.
• Clean strainers and filters, and bin any scraps.
• Refill floor drains and leave appliance doors slightly open.
• Turn off the stopcock if you’ll be away for weeks.

If you like the engineering angle

In commercial settings, trap primers are often used. These devices drip small amounts of water into traps when the system detects use.

You can install a domestic primer on a floor drain, but the glass‑and‑paper hack provides much of the same benefit. A quick visit from a neighbour to top things up can achieve a similar result without any new kit.

A quick home test if you love numbers

Wet two identical sinks so their U‑bends are filled, then cap only one using the glass‑and‑paper method. After 24 hours, weigh the kitchen paper before and after, or simply smell both drains.

The capped drain will retain moisture, while the open one will feel drier. In hotter weather, that difference increases more quickly.

Small extras that add comfort

If you like, add a drop of essential oil to the paper under the glass for a mild scent when you get back. A silicone drain cover can live in a drawer and be used all year.

A spare rubber plug is inexpensive, and it can save a lot of faff when you’re trying to pack in a hurry.