Drain smell in a Tokyo apartment: safe first steps

If you suspect gas rather than a drain smell, stop here. Do not operate an electrical switch; leave the area and follow the gas-emergency steps below. You do not need to identify an unfamiliar smell yourself.

For a clear sewage smell from a sink, bath or floor drain, run ordinary tap water into that drain first. A drain trap holds a small amount of water between the room and the waste pipe. When that water evaporates during a long absence, smells from the waste pipe can enter the apartment.

That first step is especially useful when you have just returned to Tokyo or when the smell comes from a drain you rarely use. LIXIL says a long absence or dry conditions can evaporate the trap water; its advice for an empty bath trap is to run enough shower water into it to fill it again. The Tokyo Metropolitan Government's housing guidance describes the same mechanism for sinks, baths and washing-machine pans.

Do not start by pouring in perfume, bleach or a strong drain cleaner. A deodorizer may cover the smell, but it cannot replace the missing water barrier. If you later use a cleaner, use only a product allowed by the fixture's manual and follow its label. Never mix products: Japan's Consumer Affairs Agency requires chlorine cleaners to warn that mixing them with acidic products can release dangerous chlorine gas.

First rule out a suspected gas leak

A sewage smell can be sharp, but you do not need to diagnose an unfamiliar smell yourself. If you suspect gas, stop treating it as a drain problem. Do not use flames, and do not turn lights, extractor fans or other electrical switches on or off. Open windows and doors by hand if you can do so safely, close the gas valve if it is safe to reach, leave the area, and call your gas network's emergency number from outside.

Tokyo Gas Network's instructions warn that an electrical switch can create a spark. If you are unsure which utility serves the apartment, your contract, gas bill or building manager should identify the network. Our guide to Tokyo apartment emergencies explains the wider emergency contact order. Do not try a gas-meter reset while gas may be leaking; the meter-reset guide starts only after you have confirmed there is no gas smell.

Restore the seal, then observe

Run cool or lukewarm tap water long enough to refill the trap. Do this separately for each little-used outlet: the bathroom floor drain, bath, washbasin, kitchen sink and an accessible washing-machine pan drain. You are trying to restore a water seal, not flush a blockage.

Wait a few minutes, then check the same area again. If the smell fades and stays away, a dry trap was the likely cause. Keep using that outlet normally. Before another long absence, check the fixture manual or ask the manager what the maker recommends; trap designs differ, so a method for one bath or sink may be wrong for another.

When the smell appeared tells you what to check next. A smell after weeks away points to evaporated water, so refill the trap. A smell that began immediately after cleaning points instead to a removable part that may be missing, facing the wrong way or not fully secured. More cleaning will not correct that fit.

Tokyo's sewerage bureau notes that the inverted cup-shaped part used in many bath drains sometimes gets left out. TOTO's illustrated instructions show that its removable drain piece must face the stated direction and that the cylinder holding the water seal must be secured. Put back only tenant-removable parts shown in the manual for your exact model, in the stated direction, and tighten them only as instructed.

Do not loosen the pipe beneath a sink, remove fixed trap sections, force a stuck component or improvise a seal. If you cannot identify the model or the part does not sit easily, stop and send the manager a photo.

Clean only what the manual makes accessible

Hair, soap and residue on a visible strainer can smell even when the water seal is intact. Remove hair from the catcher and wash only the accessible pieces that your fixture manual identifies. TOTO and LIXIL publish different cleaning sequences for different drain types, which is why the model-specific instructions matter.

Once the pieces are back in place, run water again to restore the seal. LIXIL's instructions for one washbasin bottle trap, for example, specify running water for 10 to 20 seconds after cleaning. Treat that timing as guidance for that design, not a rule for every Tokyo apartment.

Surface cleaning will not repair a cracked part, a failed seal or a pipe problem. It also will not clear a serious blockage. If water is rising toward the floor or cabinet, stop using the fixture and follow the first response in our Tokyo rental water-leak guide.

When to contact the building manager

Contact the landlord, rental company or building manager if the smell returns after the trap has been refilled, or if you notice any of these signs:

• repeated gurgling during ordinary drainage;
• water draining slowly or backing up;
• moisture, drips or staining beneath the sink or around the drain;
• a removable trap part that is cracked, missing, loose or will not refit as the manual shows;
• the smell affecting several drains at once or returning soon after each refill.

Send the fixture location, when the smell began, whether the apartment was unused, which drain you refilled, whether the smell improved, and whether there is gurgling, slow flow or a leak. Add a photo of the drain and any model label, plus a short video if the sound or backup is intermittent. These details help the manager decide what to inspect and whether to call a plumber.

Tokyo's sewerage bureau says an absent or malfunctioning trap can let odour flow back indoors. Until help arrives, do not use a fixture that leaks, backs up or drains very slowly, and tell the manager promptly if the smell spreads to other drains.