Floor drain or sewer smell in the bathroom? How to clean the drain

Almost every Finnish bathroom has a floor drain (lattiakaivo), and so do saunas and many utility rooms. If you come from a country where bathroom floors have no drain, it may be news that they need regular cleaning. When the bathroom smells of sewage, the floor drain is the first place to look. Here is why it happens, how to clean the drain safely, and when the problem belongs to a plumber or to your housing company.

Why does a floor drain smell?

Every floor drain, sink and toilet has a water trap. The water standing in it forms a seal that stops sewer air rising into the room. A sewer smell in the bathroom usually has one of these causes:

• A dried-out water seal. In a rarely used drain, the water evaporates and sewer air comes straight in. Sauna, utility room and guest toilet drains are typical culprits.
• Hair and soap sludge. Dirt builds up in the strainer and the trap and starts to rot, so it smells even when the seal is full.
• Loose or broken parts. If the trap insert is not seated properly or its seal is worn, sewer air gets past the water.
• A blocked vent pipe (tuuletusviemäri). The drains are ventilated through a pipe that runs up through the roof. If it is blocked, draining water can suck the seals empty.

You can usually fix the first two yourself. The last two often need a professional.

A dried-out water seal: the easy fix

If the smell comes from a drain that hasn't been used for a while, pour a few litres of water into it. Once the trap refills and the room is aired, the smell should soon go. Top up rarely used drains every week or two, and after a long trip run water into every drain and sink.

How to clean a floor drain, step by step

Floor drains come in many models, but most are cleaned the same way. You need rubber gloves, a bin bag, an old washing-up brush and some washing-up liquid.

1. Protect your hands and ventilate. Put on the gloves and switch on the extractor fan.
2. Remove the grate. It usually lifts off by hand or with a flat screwdriver used gently as a lever.
3. Empty the strainer. Lift out the strainer basket (siivilä) and put the hair and dirt in the bin bag, not down the drain.
4. Lift out the trap insert. In most modern plastic drains, the trap insert (vesilukko-osa) pulls or twists out. In old cast iron drains it may be stuck, so don't force it.
5. Wash the parts. Scrub the strainer, the insert and the inside of the drain with warm water and washing-up liquid. Don't pour boiling water into a plastic drain.
6. Check the seal. The rubber seal on the trap insert should be intact and sitting in its groove.
7. Reassemble and refill. Press the insert firmly back into place, refit the strainer and grate, and pour in a few litres of water. Check that it drains away normally.

How often should you clean it?

Empty the strainer in a shower drain every week or two, more often if anyone at home has long hair, and clean the whole drain, trap included, every few months. Washing machine and sauna drains get dirty more slowly, but their water seal dries out more easily. A drain that empties slowly is a sign that cleaning is overdue. If water stands in a sink or washbasin, see also how to unblock a sink drain.

Chemical drain cleaners: use with care

Shop-bought drain cleaners are no substitute for cleaning by hand, and an ordinary smell doesn't call for them. If you use one, follow the label closely:

• Wear gloves and eye protection, and ventilate the room.
• Never mix products or use them one after another. A chlorine-based cleaner and an acidic one, for example, can release toxic gas.
• Strong products can damage old pipes and seals.
• If it doesn't work, don't add more. Tell the plumber or the maintenance company what has gone into the drain.

When cleaning doesn't stop the smell

If the drain is clean, the trap is full and the smell persists, look elsewhere:

• The drain itself. A cracked or misplaced trap insert, or a loose drain collar (kaulus) or seal, lets sewer air bypass the water.
• The sink trap and connections. A leaking trap, a loose waste pipe connection or a badly connected appliance hose can let sewer air out. Check whether the cabinet under the sink is damp.
• The toilet. If the smell is strongest at the base of the toilet, the seal between the toilet and the sewer pipe may be leaking.
• The vent pipe. Drains that gurgle when the washing machine empties or the toilet is flushed point to a ventilation problem. In a detached house, leaves or winter frost can block the vent pipe on the roof, and the air admittance valve (alipaineventtiili) used in some houses can stick. Roof work needs proper safety equipment, so this check is often best left to a professional.

Tell the smells apart, too: sewer gas smells of rotten eggs, while a musty, earthy smell can point to moisture damage. Loose tiles, cracked grout or dark patches around the drain may mean the waterproofing is damaged.

A leaking sink trap or waste pipe connection can be fixed as one of our small plumbing jobs. If the sink is due for replacement anyway, see sink installation.

Apartments and terraced houses: who is responsible?

In a housing company (taloyhtiö), cleaning the floor drain is usually the resident's job, whether you own or rent. The drain itself, the waterproofing and the shared sewer pipes, vent stack included, are usually the housing company's responsibility. Check the maintenance responsibility table (vastuunjakotaulukko) or ask the property manager (isännöitsijä). Contact the maintenance company (huoltoyhtiö) if:

• the drain is cracked, parts are broken or the tiles around it are damaged
• the smell continues after cleaning, or it can also be smelt in other flats or the stairwell
• the drains gurgle or water comes up through the drain

If you rent, tell your landlord as well. Replacing a floor drain means connecting the waterproofing to the new drain, so it is usually done as part of a bathroom renovation. An owner who arranges that renovation must first send the housing company a renovation notice. If water has escaped around the drain into the structures, see what to do after a water leak.

Summary

1. Pour water into rarely used drains every week or two.
2. Empty the strainer often and clean the whole drain every few months.
3. If the smell persists, check the sink traps, the toilet connection and the vent pipe.
4. In a housing company, report damage and recurring smells to the maintenance company.

If the smell comes from a leaking sink trap or a loose waste pipe connection, we can repair it. See small plumbing jobs or contact us to arrange a visit.