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[Solved] Unpleasant Sewage Odor from 1960s Sink: Tried Hot Water, Kreta Granules & Enzymes – What's Next?

Htomas 20496 20
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How do I stop a recurring sewage smell from a sink after flushing the tap water?

Clean or replace the sink siphon first, because old siphons can hold sludge and even become a source of odor themselves [#18138336] [#18144741] [#18144822] Also clean the drain inlet in the wall and the overflow/overflow tubes, since hairs and muck often collect there; one suggestion was to pour a drain cleaner solution into the overflow and let it work [#18142118] [#18137201] [#18138788] Check that the siphon is assembled correctly and that the pipe connection is properly submerged/sealed, because a bad fit can let sewer air pass [#18137176] [#18138193] If the smell disappears when the sink is blocked with a stopper, that points to the sink drain/overflow or siphon rather than the main sewer [#18138324] In the thread, the problem was ultimately solved by dismantling and thoroughly cleaning the siphon, then replacing it with a new one when the old one could not be properly serviced [#18144741]
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  • #1 18137174
    Htomas
    Level 18  
    Posts: 1034
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    I live in a block from the beginning of the 60's. For some time the sink has been giving off an unpleasant odor from the sewage system after flushing the tap water. I tried to run hot water for half an hour, then I sprinkled Kreta in granules but it did not help. In the end I used Kreta Bio with enzymes, poured in 100 ml as instructed and left it overnight, then rinsed It seemed that the problem was gone, but after a few days it returned. What's next?
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  • #2 18137176
    berthold61
    Level 28  
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    Check the siphon under the sink if it has the right level, maybe you have pushed too much of a pipe inside and there is no level so the air passes through.
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  • #3 18137201
    palmus
    Level 34  
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    Often muck remains in the tubules from the overflow. Sprinkle a mole there, preferably as a solution.
  • #4 18137209
    Htomas
    Level 18  
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    berthold61 wrote:
    Check the siphon under the sink if it has the right level, maybe you have pushed too much of a pipe inside and there is no level so the air passes through.

    The vertical tube enters 0.5 cm, the horizontal one approx. 3 cm
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  • #5 18137227
    Htomas
    Level 18  
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    palmus wrote:
    Often muck remains in the tubules from the overflow. Sprinkle a mole there, preferably as a solution.

    And how to secure it so that it does not run off?
  • #6 18138193
    berthold61
    Level 28  
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    Htomas wrote:
    berthold61 wrote:
    Check the siphon under the sink if it has the right level, maybe you have pushed too much of a pipe inside and there is no level so the air passes through.

    The vertical tube enters 0.5 cm, the horizontal one approx. 3 cm

    I do not know if I understand you correctly, but this tube from the top is to be submerged below the water level by at least 3 cm.
  • #7 18138308
    piracik
    VIP Meritorious for electroda.pl  
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    berthold61 wrote:

    I do not know if I understand you correctly, but this tube from the top is to be submerged below the water level by at least 3 cm.


    Irrelevant. Siphon and it will be so. This chamber is divided inside.
  • #8 18138324
    Rezystor240
    Level 42  
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    @piracik

    Exactly as you're saying.

    The solution may not be practical, but I will write. Block the sink with the stopper and the problem will disappear, unless the stench hits the overflow.
    Doesn't it smell from other sewage holes? Can you hear gurgling in the siphon? Various things can happen.
  • #9 18138336
    KapitanSTS
    Level 30  
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    Perhaps it is worth cleaning the siphon itself.
  • #10 18138343
    Rezystor240
    Level 42  
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    @CapitanSTS

    This step should be done first.
  • #11 18138633
    ziemek56
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    palmus wrote:
    The vertical tube enters 0.5 cm, the horizontal one approx. 3 cm

    Vertical too little !!! it must be at least 5 cm below the water level in the siphon - then the buoyant odors from the sewage system will not overcome the liquid.
    It is very common that in the sewage riser (there is always a vent pipe above the top floor), for example, a pigeon settles and the gases compress a bit.
    5 cm of water = 0.005 bar. 5 m of water = 0.5 bar :)
  • #12 18138781
    piracik
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    If what you write about immersion of the tube made sense, this drawing would be wrong.
    The manufacturer states that we can pull the tube as much as 110 mm when the water surface is about 90 mm?
    Does he not know how the siphon works?

    Unpleasant Sewage Odor from 1960s Sink: Tried Hot Water, Kreta Granules & Enzymes – What's Next?

    Added after 30 [seconds]:

    ziemek56 wrote:
    Vertical too little !!! it must be at least 5 cm below the water level in the siphon - then the buoyant odors from the sewage system will not overcome the liquid.
  • #13 18138788
    palmus
    Level 34  
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    Htomas wrote:

    And how to secure it so that it does not run off?

    You're not securing. The thick solution will do its job. You can repeat that later.
    I have already seen 3 "modern" sinks, where the water flowing down the drain ran into the overflow from the bottom, then just a few hairs and it's starting to make a nest there ...
  • #14 18140535
    ziemek56
    Level 22  
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    This is a drawing - a view. It does not show the interior. You would have this cross-section.
    I put some on the drawing and you can see how the water goes.
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  • #15 18140536
    ziemek56
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    piracik wrote:
    The manufacturer states that we can pull the tube as much as 110 mm when the water surface is about 90 mm

    Because that's how much you can extend and maintain the mechanical rigidity of the connection. For the manufacturer, it is a sedimentation tank, and whether it will be a siphon depends on the immersion of the downpipe.
    piracik wrote:
    This chamber is divided inside.


    Yes, the photo above shows another one, and it can be with a partition.
    In my apartment, the settlers' chambers are not divided and there is a free passage in the "pear".
    I have exactly the ones in the drawing.
    The baffle in this model would have to be like a green line and ... it would be a bit tight at outlet 32
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  • #16 18140633
    piracik
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    ziemek56 wrote:
    For the manufacturer, it is a sedimentation tank, and whether it will be a siphon depends on the immersion of the downpipe.


    Good. You have a fantasy :)

    You see, I don't need a cross-section to infer from the documentation that the manufacturer siphon allows the tube to be pulled out so that its end is about 110 mm above the bottom of the glass siphon if at the same time this height is half the height of the drain, i.e. higher than the water level, a siphon must be structurally provided in the center. For example, through a partition or a tube as in the photo
    Unpleasant Sewage Odor from 1960s Sink: Tried Hot Water, Kreta Granules & Enzymes – What's Next?

    Settler :please:
  • #17 18142118
    hugonot11
    Level 11  
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    did you clean the pipes and the sewer inlet in the wall? hairs etc. often settle there and then it stinks, if you poured plaster into the wash basin, then take it apart carefully and clean it
  • #18 18142353
    palmus
    Level 34  
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    There is one more, unlikely reason, but still possible: my friend had a faulty wash basin and water was getting between both sides of the ceramic cast (!). The cause of the stench was undetectable until the sink was disassembled and dissected ...
    I didn't believe it until he showed me the pictures.
  • #19 18142354
    Htomas
    Level 18  
    Posts: 1034
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    hugonot11 wrote:
    did you clean the pipes and the sewer inlet in the wall? hairs etc. often settle there and then it stinks, if you poured plaster into the wash basin, then take it apart carefully and clean it

    The problem was probably the transfer. I blocked the sink with a stopper and turned on the hot water for half an hour. And then I remembered that I have K2 foam for cleaning car air conditioning somewhere. I peed, waited, rinsed and it's probably OK. Of course, I unscrewed the siphon and cleaned it thoroughly.
  • #20 18144741
    Htomas
    Level 18  
    Posts: 1034
    Rate: 151
    The topic seemed to be resolved, but not quite as it turned out. The slight stench continued to emerge. I put a wire into the sink drain, when I pulled it out, there were gray fragments of some goo stuck on it. Since the screw fastening the siphon inlet could not be moved, I opened it and dismantled the siphon. As the screw in the vice could not be unscrewed, I took it all to a DIY store and it turned out that you had to buy a whole new siphon. I felt sorry for less than PLN 30 and bought it. Having access to the drain from below, I covered it with foil and poured Kreta Bio for a few hours. Then I rinsed. I installed a new siphon, blocked the sink with the plug included in the set and let the water run for several minutes. Then I put the wire in the drain again. This time there was no muck. Smells too. So it looks like the problem is finally solved to the end. But let's wait until tomorrow :D
  • #21 18144822
    stanislaw1954
    Level 43  
    Posts: 15002
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    A several-year-old washbasin or sink siphon is sometimes worth unscrewing and thoroughly washing all parts, because despite the fact that it cuts off odors from the sewage system, it is / can cause unpleasant odors in itself.
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Topic summary

✨ The discussion revolves around a persistent sewage odor emanating from a sink installed in a 1960s building. The original poster attempted various solutions, including running hot water, using Kreta granules, and applying Kreta Bio with enzymes, but the odor returned after a few days. Responses from the community suggested checking the siphon for proper water level, cleaning the siphon and pipes, and ensuring that the vertical tube is submerged adequately to prevent odors from escaping. The poster later reported success after thoroughly cleaning the siphon, replacing it, and using Kreta Bio again, leading to the resolution of the odor issue.
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FAQ

TL;DR: “5 cm of water = 0.005 bar” is your odor barrier; fix sink smells by cleaning the overflow, servicing or replacing the siphon, and confirming the trap’s water seal. Persistent odors can indicate venting issues. [Elektroda, ziemek56, post #18138633]

Why it matters: This FAQ helps apartment dwellers with older plumbing pinpoint and fix sewer-odor sources fast.

Quick Facts

How do I quickly tell if the odor comes from the overflow or the drain?

Do a stopper test. Block the drain tightly and sniff near the overflow. If smell remains, clean the overflow. If smell stops, inspect the trap and wall inlet. “Block the sink with the stopper and the problem will disappear, unless the stench hits the overflow.” [Elektroda, Rezystor240, post #18138324]

What immersion depth should the vertical tube have in a bottle trap?

For non-baffled bottle traps, keep the downpipe at least 5 cm below the waterline to maintain the seal. That water column resists sewer gas pressure. “5 cm of water = 0.005 bar.” If the seal drops, odors pass. [Elektroda, ziemek56, post #18138633]

My trap has an internal baffle—does tube immersion depth still matter?

Baffled bottle traps create the seal internally, so visible immersion of the tube matters less. Verify by checking the trap’s diagram or manual. “This chamber is divided inside.” Still ensure the trap always holds water after use. [Elektroda, piracik, post #18138308]

How do I clean a sink overflow without it just draining away?

Use a thick, gel cleaner and let gravity work.
  1. Insert the drain stopper and fill the basin to cover the overflow slot.
  2. Using a funnel, pour a thick solution into the overflow.
  3. Wait, then flush with hot water; repeat if needed. “The thick solution will do its job.” [Elektroda, palmus, post #18138788]

What cleaning steps actually solved the odor in this thread?

The fix combined deep cleaning and a new trap. The user pulled gray goo with a wire, soaked the drain with enzyme cleaner, replaced a seized siphon, then ran water with the plug in and rechecked. No muck returned and the smell stopped. [Elektroda, Htomas, post #18144741]

Do enzymes or hot water alone fix sink odors?

They can help temporarily, but not cure buildup. One user ran hot water for 30 minutes, then dosed 100 ml of enzyme overnight. The odor returned in days until deeper cleaning and trap service were done. Treat the source, not just symptoms. [Elektroda, Htomas, post #18137174]

Should I also clean the sewer inlet in the wall?

Yes. Hair and debris often sit at the wall inlet and can smell. Remove the trap, inspect the wall socket, and clear buildup. If you previously used strong chemicals, disassemble carefully and rinse thoroughly for safety before scrubbing. [Elektroda, hugonot11, post #18142118]

Can AC-foam (e.g., K2) help clean the overflow?

Yes. One user foamed the overflow with K2 AC cleaner, waited, then flushed hot water. Combined with trap cleaning, this removed the smell. Foam clings to vertical passages and breaks biofilm in the overflow channel. [Elektroda, Htomas, post #18142354]

What if trap fittings are seized—replace or force them?

Replace them. Forcing can crack old plastic. The user could not loosen the screw even in a vise and bought a new siphon for under PLN 30, which resolved the odor. New seals and plastics restore reliability. [Elektroda, Htomas, post #18144741]

Could venting or a blocked stack cause recurring odors?

Yes. A blocked vent stack can pressurize gases and push odor past a weak seal. Birds or debris can obstruct the vent. Maintain a solid water seal in the trap to resist pressure differences and call a pro if it persists. [Elektroda, ziemek56, post #18138633]

Could the ceramic sink itself be the cause?

Rarely, yes. A faulty basin can trap water between cast layers and smell. One case only surfaced after removing and dissecting the basin. If all else fails, inspect or temporarily swap the basin to rule this out. [Elektroda, palmus, post #18142353]

How do I clean the siphon properly?

Remove and scrub it. Place a bowl, unscrew the trap, clean all parts, and reassemble with fresh seals if needed. Rinse thoroughly before reinstalling. This often eliminates odors that the trap itself harbors. “Perhaps it is worth cleaning the siphon itself.” [Elektroda, KapitanSTS, post #18138336]

What do diagrams showing 110 mm tube extension and ~90 mm water level imply?

They suggest the trap’s sealing is internal. One manufacturer diagram allowed the tube to extend 110 mm above the base while water sat around 90 mm, implying a baffle or inner tube provides the seal. Check your model’s schematic. [Elektroda, piracik, post #18138781]

Once fixed, how do I confirm the smell is gone?

Run water several minutes with the plug in, then probe the drain with a wire. If no gray slime returns and no odor appears the next day, the fix holds. Recheck overflow and wall inlet if odor recurs. [Elektroda, Htomas, post #18144741]
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