Sewage smell from soil pipe - advice needed

1 Mar 2011
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United Kingdom
Evening all,

For about the last 6-8 months I have had a horrible sewer smell coming from the cupboard where the soil pipe goes into the floor and nothing I do seems to make it go away. We have tried all sorts of cleaners down the sinks and toilet but to no avail.

We have an internal vented soil pipe in a downstairs cupboard next to my front door which runs vertically straight up and through the roof where it vents. Along the way there are a few connecting pipes from basins etc so I have drawn a quick diagram of the layout to save confusion.

As I said the smell is mainly in the cupboard where the soil stack goes into the ground. In this cupboard are where the washing machine stand pipe and pipe from the kitchen go into the soil stack.

There are no leaks that I can find and the washing machine stand pipe is clear from built up gunk. I checked the washing machine waste pipe is installed correctly which it is.

I can only guess that the smell is coming from the washing machine stand pipe because there are no smells in the kitchen so can anyone recomend a way of stopping the sewer gases coming into the house?
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Do a service wash on the washing machine, which consists of running the washing machine on it's hottest temperature and longest wash with no clothes of soap powder/liquid in the machine. Let the machine run full cycle.

This is good for the machine and all pipework, this should be done once a month.

Thanks Andy,
I do that regularly after having problems with my washing machine a few years ago, but it does not make any difference.

Any more suggestions?

I have read about an Hep Vo valve in other threads but am not sure whether this would solve my problem and it it can be put between the stand pipe and soil stack in this arrangement.
Remove the washing machine pipe out of the up-stand and block the up-stand, leave this over the weekend to see if the smell is still there.

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How is the soil stack sealed into the ground?
If with cement then this could have failed around the edge ,
Or just cracked etc.
HI Andy,

I'll give that a go and report back.


Here is photo of the connection. How can I tell if the seal has failed? There are no visible leaks.

Thanks for your help guys
I would be looking at syphon-age of the water from the washing machine trap. (negative pressure when a big slug of water, say from the WC above) passes down the vertical section creating negative pressure zone behind it.

A vertically mounted HEPvO trap (DO NOT MOUNT IT HORIZONTALLY whatever the makers say....) may well help, or fit an Anti-Vac trap to the washbasin or a 'Durgo' Air admittance valve at the top of the stack.

Hope this helps.

It is definitely some sort of screw on cap but it is bloody tight. I assume that it should be?

Thanks for your input. The top of the stack is not very accessible being as its on top of the roof ;)
I have blocked the washing machine standpipe with gaffer tape as Andy said in a previous post and the smell is definitely less noticeable.

I think I will get a hepvo trap and mount it at the bottom of the stand pipe to see if that helps.

I'll update the post once it is fitted.

Thanks again.

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