Smelly drain in sink and shower: trap, hair and cleaning without harsh chemicals

A smelly drain in the sink is most often cleaned mechanically: place a bucket under the sink, loosen the slip nuts, remove the trap, scrape out the accumulated grease and food scraps, rinse it with hot water and washing-up liquid, and reassemble. Chemical products usually won't flush out deposits in the trap. If the smell resembles sewage and the drain is infrequently used, first run water through it.

Identifying the cause by the smell

Before you start taking anything apart or pouring anything in, try to describe the smell. Each type points to a different location and different solution.

Rotten egg smell is worth attention. The American agency ATSDR describes hydrogen sulphide as a gas with this smell, also known as sewer gas, and notes that it is produced among other things by bacterial decomposition of organic matter. If such a smell persists even after running water through and cleaning the trap, contact your building manager or plumber.

Tools you'll need

• a bucket or flat bowl under the trap
• rubber or nitrile gloves
• an old toothbrush or narrow bottle brush
• washing-up liquid and hot water from the tap
• a cloth or paper towels
• a plastic hair hook for the drain or a bent wire
• a plunger (rubber suction cup) for minor blockages

How to clean the trap under the sink step by step

Most sink traps can be disassembled by hand without tools. However, designs vary, so follow the manufacturer's instructions if you have them. Tighten plastic nuts only by hand – excessive force can damage the threads or seals.

1. Empty the cabinet under the sink and place a bucket under the trap. There is always water in the trap.
2. If a dishwasher or washing machine is connected to the trap, do not run them until cleaning is finished.
3. Loosen the slip nuts, usually the one at the sink outlet and the one at the waste pipe in the wall. For a bottle trap, simply unscrew the lower container.
4. Carefully remove the trap and pour its contents into the bucket. Remember where the seals were, or take a photo.
5. Scrape the accumulated grease and scraps into a general waste bin, not back into the sink.
6. Scrub the trap with a brush in hot water and washing-up liquid, including the branch for the appliance.
7. Also use the bottle brush on the drain outlet from above and the short length of pipe in the wall that you can reach.
8. Check the seals. If they are cracked, hardened or deformed, buy the same type and size.
9. Reassemble the trap, tighten the nuts by hand and run the water. Watch for a few minutes to see if the joints leak.

If the smell persists after cleaning the trap, the problem is usually further in the pipes. Do not attempt to fix the main stack yourself – contact your building manager.

Drain in the shower and bath: hair and soap

In the shower, smell usually stems from a clump of hair matted with soap and cosmetic residue. This traps further debris and smells in damp conditions.

1. Remove the drain cover or shower tray grating. Under the grating, you'll usually find a removable strainer or U-bend extension; find the procedure in the manufacturer's instructions.
2. Wearing gloves, pull out the hair by hand or with a plastic hair hook.
3. Scrub removable parts with a brush and washing-up liquid and rinse.
4. Return all parts to their exact positions. A missing or incorrectly fitted U-bend component can allow sewer smell through.
5. Run water through the drain to refill the water seal.

A hair-catching strainer that you empty after each wash will replace most major cleaning. If you're also dealing with film on glass or fittings, the article how to clean a shower enclosure will help, and deposits on the shower head and taps are addressed in removing limescale.

Sewer smell from an infrequently used drain

The trap works because water remains in it and separates the flat from the sewer. When a drain isn't used for a long time – for example in a guest room, a holiday home or a flat during a long absence – the water can evaporate and sewer smell can enter.

• Run water through every drain for a minute, including floor wastes in the bathroom or laundry room.
• If the smell disappears within a few hours, the cause was a dried-out water seal. Then regularly rinse infrequently used drains.
• If it returns soon after filling, check that the trap and hoses are sealed properly and that there are no leaks anywhere.

When to use chemicals and how to do it safely

Chemical cleaners make sense mainly where the drain runs slowly and the trap can't be disassembled. For trap smell from deposits, mechanical cleaning is more reliable. The Toxicological Information Centre notes that drain cleaners contain alkalis, most commonly sodium hydroxide, which can irritate or corrode mucous membranes.

• Read the entire label and follow the dosage and exposure time.
• Wear gloves and eye protection and ensure ventilation.
• Don't pour the cleaner into a drain containing water with another product, and don't use a plunger whilst the cleaner is in the drain as it could splash out.
• Never mix chlorine-based products with acids or ammonia. TIS warns on WC cleaners containing sodium hypochlorite and acids that they must not be mixed as there is a risk of gaseous chlorine being released. Also, the CDC warns that chlorine bleach can release gaseous chlorine when mixed with other cleaning products and recommends that cleaning products not be mixed.
• If one product doesn't work, don't add another immediately. First rinse the drain thoroughly with water according to the instructions on the first product.
• Test the product first on a hidden area if it could come into contact with the sink or tub surface, and follow the manufacturer's instructions for the sink.

Other dangerous combinations are summarised in the article cleaning products never to mix. Store drain cleaners in their original containers out of children's reach; details can be found in the article how to store cleaning products safely.

If the cleaner gets in your eye, rinse the eye thoroughly with clean water for a long time, immediately call TIS or a doctor and follow the instructions on the label. If drain cleaner is swallowed, do not induce vomiting – give the person water, milk or tea; according to TIS, activated charcoal is not suitable in this case. Contact the Toxicological Information Centre on 224 91 92 93.

If you want products with a safer composition, the American EPA Safer Choice programme lists biological products for drain maintenance among its certified products. However, these won't replace cleaning the trap if there are deposits in it.

Preventing drain smell

Prague Water and Sewerage notes that grease and oils accumulate on sewer walls, harden and collect more debris. Similarly, wet wipes tend to stick in pipes. The same process begins in your own trap.

• Wipe grease from pans with a paper towel and throw it away, pour oil into a sealable container.
• Put a strainer over the sink for food scraps and empty it into the food waste or bin.
• Use a hair strainer in the shower and empty it after each wash.
• Once a month or every two months, remove and scrub the trap under the sink and the strainer in the shower.
• Rinse infrequently used drains with water at least once every few weeks.

If you don't want to do regular kitchen and bathroom cleaning yourself, you can order household cleaning from Úklid 1-2-3; you'll find the scope and prices in the price list. However, a blocked pipe beyond the trap is a job for a plumber.