Dangerous drain smells

23 May 2007
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United Kingdom
Drains Smells
For several months (yes!) we've had drains smells coming into our house. What concerns me is that I read elsewhere in the forum about the toxic and explosive nature of sewer gases seeping into a house! We've had the drains jetted out, and a full camera inspection, and there are no leaks. So they are apparently not the cause of our problems.

Our Installation
So the focus turns to inside the house. We have a bathroom and kitchen above each other. There are no drains smells in the bathroom. We also have a downstairs WC (with macerator) and washbasin, the waste for which is transported by smaller pipes, passing a connection to a standpipe for a washing machine. Sink and standpipe have u-bends. Macerator wc is flushed out almost daily with bleach.

A dishwasher is connected to one of the nibs on the sink waste (above the trap). Everything on the installation seems to be discharging OK into the drains.

We get serious smells in the cupboard under the stairs (standpipe?), in the dining room next to it, in the downstairs WC and in the kitchen particularly. There are no blockages we are aware of. The Macerator WC seems to be working fine, and we've only ever used it for urinating (such a claustrophobic room!) The smells seem to be worst when we're using the washing machine.

This leads me to question:

1. Is the soil vent pipe blocked? I guess not, because we are experiencing no blockages, and water is not being sucked out of the toilet pans. Is this a fair diagnosis, or could the SVP still be blocked?

2. Is it the standpipe? Is the force of the waste from the washing machine clearing its own trap and letting smells in? Should the standpipe be any particular height?

3. Subsidence and fall. Has the fall for the drains on the lower floor been affected by subsidence? Could the fall be adequate to let the installation drain OK, but passing sewage from the next door house back up into our system?

4. Leaking Pipework. Has the pipework from the macerating wc/standpipe been broken somewhere and be leaking out under the floor? (All the rooms have a raised ventilated underfloor?) How can we check this out - there seems to be no access to the underfloor space.

5. Is there anything I've forgotten?

Any pointers that would help me to eliminate anything and focus on the likely cause would be appreciated.
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Lift the boards/remove plasterboard and check the whole route of the waste pipe from the Sani-sh*te - sometimes they become incontinent.

Are you sure this waste pipe isn't connected in the wrong place so it back flows into the traps?

Next time you are away for a day or two tape over all the overflows/standpipes and put the waste plugs in. See if the smell is still there when you come back.
SOmethng else to try would be a coloured smoke bomb in the manhole. Will sometimes find a route you hadn't thought of.
Check things like the wc overflow if it has one. Sometimes they provide a path for whiffs.

You aren't alone - I know 2 houses where hours have been spent trying to find the source of smells - without any progress.
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Thanks Chris R and GasGuru.

The smoke bomb sounds a good idea - perhaps I'll try that for a little more clarity on site. That would certainly indicate whether the SVP is the problem because it should smoke (at least to some extent) like an chimney.

Regrettably I can't strip anything down myself because the house is rented. But it's our responsibility to keep the plumbing and drains clear and to ensure we have not caused a blockage. From there the landlords step in.

Any other suggestions welcome in the meantime.

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